Externally-driven joint structure

ABSTRACT

A modularized externally-driven joint structure that can be used for general purposes. In one aspect, an externally-driven joint structure includes: a shaft member that extends in an axial direction; and a plurality of rotatable members that are arranged along the axial direction, and are coupled with each other by the shaft member in an axially rotatable manner. Each of the rotatable members includes a pair of face portions that face each other in the axial direction, a side wall portion that is arranged along the outer circumferential edges of the pair of face portions, and at least one coupling portion that is arranged at the face portions or the side wall portion, and is coupled with a link member constituting a link of a robot.

BACKGROUND OF THE INVENTION Technical Field

The present invention relates to a technique of an externally-drivenjoint structure.

Background Art

Patent Literature 1 proposes a joint structure of a module-typemanipulator. Specifically, the joint structure disclosed in PatentLiterature 1 has a built-in motor, and includes attachment faces thatcan be coupled with another joint structure respectively at two pointsconsisting of a circumferential face and an end face of a rotatablemember that rotates in accordance with the rotation of the motor.Accordingly, a plurality of joint structures can be coupled with eachother, and thus it is possible to form a manipulator having amulti-joint structure.

Furthermore, Patent Literature 2 proposes a multiaxial joint in which adistal joint part and a proximal joint part are connected such that theycan axially pivot and swivel via a rotary pivot joint and a rotaryswivel joint that are connected to each other in series. According tothis multiaxial joint, it is possible to realize a joint having a highdegree of freedom in two directions in a link mechanism of a robot.

CITATION LIST—PATENT LITERATURES

Patent Literature 1: JP 562-282886A

Patent Literature 2: JP 2010-255852A

SUMMARY OF THE INVENTION Technical Problem

Joint structures that can be used for link mechanisms of robots such asexoskeletal robots or robot arms include joint structures with abuilt-in actuator (e.g., Patent Literature 1) that are directly coupledwith a drive source or that have a built-in drive source, andexternally-driven joint structures (e.g., Patent Literature 2) that aredisconnected from a drive source and that are driven by an externalforce transmitted from an external device such as a link member coupledthereto.

Joint structures with a built-in actuator are internally provided with ahousing for accommodating an actuator such as a motor for directlydriving the joint structures, and thus the size becomes relativelylarge. Furthermore, their shape, structure, drive direction, and thelike are limited due to the built-in actuator. Thus, use situations ofthe joint structures with a built-in actuator are limited.

Meanwhile, there is no such a limitation on externally-driven jointstructures, and thus they can be relatively freely designed according toa link mechanism that is to be formed. Thus, externally-driven jointstructures can be used in various situations, and various linkmechanisms can be formed using the externally-driven joint structures.

However, conventionally, externally-driven joint structures are in manycases individually designed so as to be optimal for each use situation,and they are seldom modularized. That is to say, externally-driven jointstructures that can be used for general purposes have rarely beendeveloped.

An aspect of the present invention has been made in view of thesecircumstances, and it is an object thereof to provide a modularizedexternally-driven joint structure that can be used for general purposes.

Solution to Problem

In order to solve the above-described problems, the present inventionemploys the following configurations.

That is to say, an aspect of the present invention is directed to anexternally-driven joint structure including: a shaft member that extendsin an axial direction; and a plurality of rotatable members that arearranged along the axial direction, and are coupled with each other bythe shaft member in an axially rotatable manner, wherein each of therotatable members includes a pair of face portions that face each otherin the axial direction, a side wall portion that is arranged along outercircumferential edges of the pair of face portions, and at least onecoupling portion that is arranged at the face portions or the side wallportion, and is coupled with a link member constituting a link of arobot.

With this configuration, a plurality of rotatable members are coupledwith each other in an axially rotatable manner. Moreover, each of therotatable members includes at least one coupling portion for coupling alink member constituting a link of a robot.

Thus, it is possible to couple a plurality of link members via the jointstructure according to the above-described configuration, by couplingdifferent link members with different rotatable members. Furthermore,when the link members are moved by an external force acting fromactuators or the like, the rotatable members coupled with the linkmembers can axially rotate in accordance with the rotation of the linkmembers.

That is to say, the joint structure according to the above-describedconfiguration can be driven by an external force transmitted from thelink members, and thus it is possible to change a positionalrelationship between the link members coupled with different rotatablemembers. Accordingly, with this configuration, it is possible to providea modularized externally-driven joint structure that can be used forgeneral purposes.

Furthermore, as another mode of the externally-driven joint structureaccording to the above-described aspect, it is possible that at leastone rotatable member of the plurality of rotatable members includes aplurality of the coupling portions arranged at the side wall portion.With this configuration, a plurality of link members can be coupled witha side wall portion of at least one rotatable member, and thus it ispossible to realize a complex link mechanism such as a parallel-linkedScott Russell mechanism, which will be described later.

Furthermore, as another mode of the externally-driven joint structureaccording to the above-described aspect, it is possible that at leastone rotatable member of the plurality of rotatable members includes atleast one coupling portion arranged at either one of the pair of faceportions, and other rotatable members of the plurality of rotatablemembers include at least one coupling portion arranged at the side wallportion. With this configuration, the link connecting direction can bechanged between a link member coupled with a face portion of at leastone rotatable member and a link member coupled with a side wall portionof another rotatable member. Accordingly, the link connecting directioncan be changed without a special structure, and thus the link mechanismthat is to be constructed can be made compact on the whole.

Furthermore, as another mode of the externally-driven joint structureaccording to the above-described aspect, it is possible that the faceportions of the rotatable members are provided with a recess portionwith a shape that allows a bearing in the shape of a ring that receivesa force that acts in the axial direction to be accommodated betweenrotatable members that are adjacent to each other in the axialdirection. With this configuration, it is possible to provide amodularized joint structure that can be reinforced in the axialdirection by a bearing.

Furthermore, as another mode of the externally-driven joint structureaccording to the above-described aspect, it is possible that an encoderfor detecting a relative rotational angle between the rotatable membersthat are adjacent to each other in the axial direction is furtheraccommodated between the recess portions of the adjacent rotatablemembers. With this configuration, an encoder for detecting a rotationalangle is built in the joint structure. Thus, it is possible to provide acompact and modularized joint structure that can detect an angle.

Furthermore, as another mode of the externally-driven joint structureaccording to the above-described aspect, it is possible that the recessportions are formed in the shape of a circular ring, bases of innercircumferential faces of the recess portions are provided with a stepportion in the shape of a circular ring extending inward in a radialdirection from the inner circumferential faces, a face portion of arotatable member that faces the recess portions, the rotatable memberbeing adjacent to the rotatable members, is provided with a projectingportion in the shape of a circular ring with a diameter smaller thanthat of the recess portions, a base of an outer circumferential face ofthe projecting portion is provided with a step portion in the shape of acircular ring extending outward in the radial direction from the outercircumferential face of the projecting portion, and a cross rollerbearing as the bearing in the shape of a ring is arranged so as to besupported by the inner circumferential face of the recess portion, aface along the axial direction of the step portion of the recessportion, the outer circumferential face of the projecting portion, and aface along the axial direction of the step portion of the projectingportion. With this configuration, since a cross roller bearing is used,it is possible to increase the outer diameter of the shaft membercompared with the case in which a thrust bearing is used. Accordingly,the rigidity of the shaft member can be improved.

Furthermore, as another mode of the externally-driven joint structureaccording to the above-described aspect, it is possible that the jointstructure includes two rotatable members, the coupling portions of therotatable members are arranged symmetric about the axial direction suchthat, even when the joint structure is reversed about an axis that isperpendicular to the axial direction, the joint structure can be usedwhile a positional relationship between the link members is maintained,one of the two rotatable members is formed in one piece with the shaftmember, the other rotatable member of the two rotatable members has athrough hole into which the shaft member is allowed to be inserted, anda radial bearing is arranged so as to be interference-fitted to theshaft member and clearance-fitted to an inner circumferential wall ofthe through hole, or so as to be clearance-fitted to the shaft memberand interference-fitted to the inner circumferential wall of the throughhole. With this configuration, it is possible to provide a jointstructure that can be applied to situations with different loadconditions such as unbalanced loads and stationary loads, because thestructure is symmetric about the axial direction. In this case, thecoupling portions can be coupled with the same type of link members.Furthermore, following link mechanisms can be constructed using thejoint structure according to this embodiment. That is to say, an aspectof the present invention is directed to a link mechanism including: twoor more joint structures according to this embodiment; and a link memberthat is coupled with the coupling portions of the joint structures,wherein two joint structures that are adjacent to each other via thelink member are arranged such that one of the joint structures is usedin a state of being reversed about an axis that is perpendicular to theaxial direction with respect to the other joint structure so that therotatable members face each other in the direction that is perpendicularto the axial direction. With this configuration, it is possible toconstruct a link mechanism that is compact in the width direction.

Furthermore, as another mode of the externally-driven joint structureaccording to the above-described aspect, it is possible that the jointstructure includes two rotatable members, the coupling portions of therotatable members are arranged symmetric about the axial direction suchthat, even when the joint structure is reversed about an axis that isperpendicular to the axial direction, the joint structure can be usedwhile a positional relationship between the link members is maintained,the shaft member is formed separately from the two rotatable members,the rotatable members each have a through hole into which the shaftmember is allowed to be inserted, and a radial bearing is arrangedbetween the shaft member and the rotatable members so as to beinterference-fitted to the shaft member and clearance-fitted to an innercircumferential wall of the through hole, or so as to beclearance-fitted to the shaft member and interference-fitted to theinner circumferential wall of the through hole. With this configuration,it is possible to provide a joint structure that is symmetric about theaxial direction.

Furthermore, as another mode of the externally-driven joint structureaccording to the above-described aspect, it is possible that the jointstructure includes three or more rotatable members, and the couplingportions of at least two rotatable members of the three or morerotatable members are coupled with a same link member. With thisconfiguration, one link member is supported by a plurality of rotatablemembers, and thus an external force that acts from the link member canbe dispersed between the rotatable members. Accordingly, with thisconfiguration, even when a relatively large force acts from a linkmember, deformation of the shaft member of the joint structure can besuppressed.

Furthermore, as another mode of the externally-driven joint structureaccording to the above-described aspect, it is possible that couplingbetween the coupling portions and the link member is constituted by amagnet. With this configuration, it is easy to couple the rotatablemembers and the link member with each other, and thus it is easy toproduce a link mechanism.

Furthermore, as another mode of the externally-driven joint structureaccording to the above-described aspect, it is possible that therotatable members have at least one coupling portion arranged at theside wall portions, the side wall portions of the rotatable members areformed in the shape of a cylinder, and the coupling portions arranged atthe side wall portions have a shape obtained by cutting, in a tangentialdirection, arc portions of the side wall portions. With thisconfiguration, it is possible to provide a joint structure that can bemore easily produced through lathe machining or the like. Note that aside wall portion being in the shape of a cylinder refers to a state inwhich the outer shape of the side wall portion is cylindrical, exceptfor the portion obtained by cutting for forming the coupling portion.

Furthermore, as another mode of the externally-driven joint structureaccording to the above-described aspect, it is possible that the sidewall portions of the rotatable members have a height that matches athickness of the link member. With this configuration, it is possible toprovide a joint structure that can form a compact link mechanism.

Furthermore, as another mode of the externally-driven joint structureaccording to the above-described aspect, it is possible that thecoupling portions arranged at the side wall portions have a projectingportion projecting outward in the radial direction at a center in thetangential direction, in conformity with a recess portion provided at acenter of an end face of the link member. With this configuration, theportion obtained by cutting as a coupling portion in each rotatablemember can be arranged on the outer side in the radial direction, andthus it is possible to provide a joint structure in which a bearing witha relatively large diameter can be arranged.

Furthermore, as another mode of the externally-driven joint structureaccording to the above-described aspect, it is possible that areinforcing plate for supporting a coupling region of the couplingportion arranged at the side wall portion of the rotatable member andthe link member is provided on at least one of both sides in the axialdirection of the coupling region. With this configuration, it ispossible to provide a joint structure that is unlikely to be broken bytwisting.

Furthermore, as another mode of the externally-driven joint structureaccording to the above-described aspect, it is possible that each of therotatable members has a plurality of the coupling portions at the sidewall portion, and the plurality of coupling portions are arrangedsymmetric about an axis in each of the rotatable members. With thisconfiguration, it is possible to provide a joint structure that can beused while a positional relationship between the link members ismaintained even when the joint structure is axially rotated.

Furthermore, an aspect of the present invention is directed to a linkmechanism including: the joint structure according to any one ofabove-described aspects; and a link member that is coupled with thecoupling portion arranged at the side wall portions of the rotatablemembers of the joint structure, wherein the side wall portions of therotatable members of the joint structure include a wire-driving grooveportion, a fixture is attached to the link member, and a wire that isdriven by an external drive source is arranged along the wire-drivinggroove portion, and the end portion of the wire is fixed to the fixture.

Advantageous Effects of Invention

According to the present invention, it is possible to provide amodularized externally-driven joint structure that can be used forgeneral purposes.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view schematically showing an example of a jointstructure according to an embodiment;

FIG. 2 is a cross-sectional view schematically showing an example of thejoint structure according to the embodiment;

FIG. 3 schematically shows an example of a state in which the jointstructure according to the embodiment is exploded;

FIG. 4 is a partially enlarged view schematically showing an example ofa coupling portion of the joint structure according to the embodiment;

FIG. 5A is a cross-sectional view schematically showing an example of astate before a link member is coupled with the coupling portion of arotatable member according to the embodiment;

FIG. 5B is a cross-sectional view schematically showing an example of astate after the link member is coupled with the coupling portion of therotatable member according to the embodiment;

FIG. 6 schematically shows an example of a coupling state between thecoupling portion of the rotatable member according to the embodiment andan end face of the link member;

FIG. 7A is a perspective view schematically showing an example of arobot (Scott Russell mechanism) using the joint structure according tothe embodiment;

FIG. 7B is a side view schematically showing an example of the robot(Scott Russell mechanism) using the joint structure according to theembodiment;

FIG. 8 is a perspective view schematically showing an example of a robot(wire driving mechanism) using the joint structure according to theembodiment;

FIG. 9A is a perspective view schematically showing an example of arobot (delta robot) using the joint structure according to theembodiment;

FIG. 9B is a perspective view schematically showing an example of therobot (delta robot) using the joint structure according to theembodiment;

FIG. 10 is a cross-sectional view schematically showing an example of ajoint structure according to another embodiment;

FIG. 11 is a perspective view schematically showing an example of ajoint structure according to another embodiment;

FIG. 12 is a perspective view schematically showing an example of arobot (Scott Russell mechanism) using a joint structure according toanother embodiment;

FIG. 13 is a cross-sectional view schematically showing an example of ajoint structure according to another embodiment;

FIG. 14 is a perspective view schematically showing an example of ajoint structure according to another embodiment;

FIG. 15 is a cross-sectional view schematically showing an example of ajoint structure according to another embodiment;

FIG. 16A schematically shows an example of a joint structure accordingto another embodiment;

FIG. 16B is a partial cross-sectional view (a cross-section taken alongthe line C-C in FIG. 16A) schematically showing an example of a jointstructure according to another embodiment;

FIG. 17 is a perspective view schematically showing an example of arotatable member according to another embodiment; and

FIG. 18 is a cross-sectional view schematically showing an example of ajoint structure according to another embodiment.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Hereinafter, an embodiment according to an aspect of the presentinvention (hereinafter, also described as “the present embodiment”) willbe described based on the drawings. The present embodiment describedbelow is, however, to be considered in all respects as illustrative ofthe present invention. It is to be understood that various improvementsand modifications can be made without departing from the scope of thepresent invention. In other words, in implementing the presentinvention, specific configurations that depend on the embodiment may beemployed as appropriate.

§ 1 Configuration Example

First, an externally-driven joint structure 1 according to the presentembodiment will be described with reference to FIGS. 1 and 2 . FIG. 1 isa perspective view schematically showing an example of the jointstructure 1 according to the present embodiment. FIG. 2 is across-sectional view schematically showing an example of the jointstructure 1 according to the present embodiment. In FIG. 2 , hatching isused in order to identify each constituent element. This hatching is forthe sake of ease of description, and is not for specifying the materialor the like of each constituent element. The same applies to othercross-sectional views using hatching.

As shown as an example in FIGS. 1 and 2 , the joint structure 1according to the present embodiment includes a shaft member 13 thatextends in an axial direction (the left-right direction in FIG. 2 ) andtwo rotatable members (11 and 12) that are arranged along the axialdirection and are rotatably coupled with each other via the shaft member13. As described later, the joint structure 1 according to the presentembodiment does not include a housing for accommodating an actuator suchas a motor, and is driven by a separate drive source. Hereinafter, eachconstituent element will be described. In the description below, for thesake of ease of description, the two rotatable members (11 and 12) arealso referred to as a first rotatable member 11 and a second rotatablemember 12 respectively. Furthermore, in FIG. 1 , for the sake of ease ofdescription, each direction is indicated using an x axis, a y axis, anda z axis. The x axis refers to the axial direction of the shaft member13, and the y axis and the z axis each refer to an example of adirection that is perpendicular to the axial direction of the shaftmember 13.

Shaft Member

First, the shaft member 13 will be described. As shown as an example inFIG. 2 , the shaft member 13 according to the present embodiment isformed in one piece with the first rotatable member 11. Specifically,the shaft member 13 is coupled in one piece with the center of a secondface portion 112, which will be described later, of the first rotatablemember 11, and extends in a direction that is away from the second faceportion 112. Accordingly, in the present embodiment, the secondrotatable member 12 is coupled with the second face portion 112 side ofthe first rotatable member 11.

Furthermore, the shaft member 13 according to the present embodiment isformed in the shape of a cylinder, and includes a hollow portion 132 inthe shape of a column that extends through the axial direction. Thehollow portion 132 is arranged at the center in a direction that isalong the radius of the shaft member 13 (hereinafter, it is alsoreferred to as a “radial direction”), and extends in the axial directionthrough the shaft member 13 and the first rotatable member 11. A malethread (not shown) is formed on the outer circumferential wall of theupper end portion (the end portion on the left side in FIG. 2 ) of theshaft member 13 such that a fastener 131 (e.g., a nut) in the shape of acircular ring whose inner circumferential wall is provided with a femalethread can be attached to the male thread.

Rotatable Members

Next, the rotatable members (11 and 12) will be described. First, thefirst rotatable member 11 will be described. The first rotatable member11 according to the present embodiment includes a pair of face portions(111 and 112) that face each other in the axial direction and a sidewall portion 113 that is arranged along the outer circumferential edgesof the pair of face portions (111 and 112). Hereinafter, for the sake ofease of description, the pair of face portions (111 and 112) are alsoreferred to as a first face portion 111 and a second face portion 112.

In the present embodiment, the face portions (111 and 112) are formed inthe shape of a circle, and the height (the length in the left-rightdirection in FIG. 2 ) of the side wall portion 113 is slightly shorterthan the diameter of each of the face portions (111 and 112). Thus, thefirst rotatable member 11 is formed in the shape of a cylinder with alow height (length in the left-right direction in FIG. 2 ). The firstface portion 111 arranged on the outer side is formed as a flat face.Meanwhile, the second face portion 112 arranged on the second rotatablemember 12 side has a circular ring-like recess portion 115 around theshaft member 13.

Furthermore, in the present embodiment, the side wall portion 113 isprovided with two coupling portions 21. Specifically, the two couplingportions 21 are arranged at positions at 180 degrees about the center inthe surface direction of the face portions (111 and 112). A Link member31 constituting a link of a robot such as an exoskeletal robot or arobot arm is coupled with the coupling portions 21. The robot has a linkmechanism and includes a machine that is driven at a degree of freedomof 1 or more.

The method for coupling each coupling portion 21 and the link member 31according to the present embodiment will be described later in detail.Schematically, as shown as an example in FIG. 1 , each coupling portion21 has a groove portion 211 in the shape of an inverted T extendingthroughout a tangential direction that is perpendicular to the radialdirection, and a wedge (a wedge member 32, which will be describedlater) is attached to the groove portion 211. The link member 31 with asubstantially H-shaped cross-section is coupled via the wedges to thecoupling portion 21.

Next, the second rotatable member 12 will be described. The secondrotatable member 12 according to the present embodiment hassubstantially the same shape as the first rotatable member 11 excludingthe shaft member 13. That is to say, the second rotatable member 12according to the present embodiment includes a pair of circular faceportions (121 and 122) that face each other in the axial direction and aside wall portion 123 that is arranged along the outer circumferentialedges of the pair of face portions (121 and 122). The face portions (121and 122) have the same diameter as the face portions (111 and 112) ofthe first rotatable member 11, and the side wall portion 123 has thesame height (the same length in the axial direction) as the side wallportion 113 of the first rotatable member 11. Furthermore, the side wallportion 123 of the second rotatable member 12 is provided with twocoupling portions 21 are arranged at positions at 180 degrees about thecenter in the surface direction of the face portions (121 and 122).

Contrary to the first rotatable member 11, the second rotatable member12 has a through hole 124 in the shape of a column that extends throughthe axial direction, at the center in the surface direction of each ofthe face portions (121 and 122). The through hole 124 has a diameterthat is larger than the outer diameter of the shaft member 13 such thatthe second rotatable member 12 can be attached to the shaft member 13.Accordingly, the second rotatable member 12 is configured such that, ina state where radial bearings 15 are arranged between the innercircumferential wall of the second rotatable member 12 and the outercircumferential wall of the shaft member 13, the shaft member 13 can beinserted into the through hole 124. The second rotatable member 12 andthe first rotatable member 11 are coupled with each other in an axiallyrotatable manner, by inserting the shaft member 13 into the through hole124 of the second rotatable member 12, and then attaching the fastener131 to the upper end portion of the shaft member 13. The side faceportions (113 and 123) of the rotatable members (11 and 12) have a shapethat is symmetric about a plane perpendicular to the axial direction ofthe shaft member 13 such that the outer shape of the rotatable members(11 and 12) is bilaterally symmetric. The radial bearings 15 may beinterference-fitted to the shaft member 13 and clearance-fitted to theinner circumferential wall of the through hole 124, or may beclearance-fitted to the shaft member 13 and interference-fitted to theinner circumferential wall of the through hole 124.

The radial bearings 15 can receive a force that acts in the radialdirection. As shown as an example in FIG. 2 , in the present embodiment,two radial bearings 15 are arranged in a line in the axial directionbetween the inner circumferential wall of the second rotatable member 12and the outer circumferential wall of the shaft member 13. The innercircumferential wall of the second rotatable member 12 is provided withan interlock projecting portion 125 projecting inward in the radialdirection, and the radial bearings 15 are positioned by beinginterlocked with the interlock projecting portion 125 in the axialdirection.

At this time, the inner diameter of the radial bearings 15 issubstantially the same as the outer diameter of the shaft member 13, andthe fastener 131 prevents the radial bearing 15 arranged on the outerside (the left side in FIG. 2 ) from being detached from the shaftmember 13. Accordingly, the second rotatable member 12 is prevented frombeing detached from the shaft member 13, via the interlock projectingportion 125 by the radial bearings 15 and the fastener 131. Thus, evenwhen the outer diameter of the fastener 131 is smaller than the diameterof the through hole 124, the second rotatable member 12 can be preventedfrom being detached. Accordingly, the outer diameter of the fastener 131may be larger than or smaller than the diameter of the through hole 124.

Furthermore, in the present embodiment, the first face portion 121arranged on the first rotatable member 11 side is provided with acircular first recess portion 126 corresponding to the recess portion115 of the second face portion 112 of the first rotatable member 11 thatfaces the first face portion 121. That is to say, the first recessportion 126 has the same diameter as the recess portion 115, and thefirst recess portion 126 and the recess portion 115 are positionedadjacent to each other in the axial direction to form a circularring-like internal space. The first recess portion 126 of the secondrotatable member 12 and the recess portion 115 of the first rotatablemember 11 respectively correspond to “recess portions” of the presentinvention. The internal space defined by the first recess portion 126and the recess portion 115 accommodates a thrust bearing 14 and anencoder 16. The constituent elements accommodated in the internal spacewill be described later.

Meanwhile, the second face portion 122 is provided with a second recessportion 127 with a diameter that is smaller than the diameter of thefirst recess portion 126. The diameter of the second recess portion 127is larger than the outer diameter of the fastener 131. Thus, when usingthe fastener 131 to prevent detachment of the second rotatable member 12that has been attached to the shaft member 13, the fastener 131 isprevented from projecting significantly outward (leftward in thedrawing) from the second face portion 122 of the second rotatable member12, by the height (the length in the left-right direction in FIG. 2 ) ofthe second recess portion 127.

Furthermore, in the present embodiment, the side wall portion 123 isprovided with two wire-driving groove portions 129 that are arranged ina line in the axial direction and each extend in the circumferentialdirection. Wires for pulling and driving the joint structure 1 arearranged respectively along the wire-driving groove portions 129. Thedriving by pulling wires will be described later.

The shaft member 13 and the rotatable members (11 and 12) can beproduced using a known method such as cutting or injection molding.Furthermore, the shaft member 13 and the rotatable members (11 and 12)can be produced as appropriate using a 3D printer. The material of theshaft member 13 and the rotatable members (11 and 12) may be selected asappropriate according to an embodiment, and examples thereof includemetals such as aluminum and titanium and resins such as engineeringplastic.

Thrust Bearing and Encoder

Next, the constituent elements accommodated in the internal spacedefined by the recess portions (115 and 126) of the rotatable members(11 and 12) that are adjacent to each other in the axial direction willbe described with reference to FIG. 3 as well. FIG. 3 schematicallyshows an example of a state in which the joint structure 1 according tothe present embodiment is exploded. The recess portions (115 and 126)are formed to define a shape that allows the thrust bearing 14 and theencoder 16 to be accommodated, and thus, as described above, the thrustbearing 14 and the encoder 16 are accommodated in the internal spacedefined by the recess portions (115 and 126).

The thrust bearing 14 can receive a force that acts in the axialdirection (the thrust direction). The thrust bearing 14 is generallyconfigured such that a holding unit holding a plurality of rotatingcomponents is held between a housing washer and a shaft washer. The typeof rotating components of the thrust bearing 14 may be selected asappropriate according to an embodiment, and examples thereof includeballs and rollers. However, the type of the thrust bearing 14 is notlimited to those including rotating components, and may be those notincluding rotating components, such as oilless bushes or oillessbearings. The same applies to the radial bearings 15 described above.

As shown as an example in FIG. 2 , the thrust bearing 14 is formed inthe shape of a ring, and the outer diameter of the thrust bearing 14 issubstantially the same as the diameter of each of the recess portions(115 and 126). Meanwhile, the inner diameter of the thrust bearing 14 islarger than the outer diameter of the shaft member 13, and thus acircular ring-like gap portion 116 is formed so as to surround the shaftmember 13, between the inner circumferential wall of the thrust bearing14 and the outer circumferential wall of the shaft member 13.

In the present embodiment, as shown as an example in FIGS. 2 and 3 , thegap portion 116 accommodates the encoder 16 capable of detecting arelative rotational angle between the adjacent rotatable members (11 and12). Specifically, the encoder 16 of the optical reflection typeincluding a scale 161 and a detecting element 162 is accommodated in thegap portion 116. The scale 161 and the detecting element 162 arearranged in the gap portion 116 as follows.

That is to say, as shown as an example in FIG. 2 , a circular ring-likeplate 142 with the same outer diameter as the thrust bearing 14 isarranged on the second rotatable member 12 side of the thrust bearing14. The bottom face of the first recess portion 126 of the secondrotatable member 12 is provided with a projecting portion 128 projectingtoward the first rotatable member 11 side (to the right side in FIG. 2), and the bottom face of the plate 142 is provided with a hole portion143 corresponding to the projecting portion 128. Thus, the plate 142 ispositioned by the projecting portion 128.

As shown as an example in FIG. 2 , the inner portion in the radialdirection of the plate 142 projects in the shape of a circular ringtoward the first rotatable member 11. The outer diameter of theprojecting portion is the same as the inner diameter of the thrustbearing 14, and the inner diameter of the projecting portion issubstantially the same as or slightly larger than the outer diameter ofthe shaft member 13. Accordingly, the projecting portion is fitted intothe hollow portion of the thrust bearing 14. The circular ring-likescale 161 is attached to the end face of the projecting portion on thefirst rotatable member 11 side.

Meanwhile, a circular ring-like washer 141 with the same outer diameterand inner diameter as the thrust bearing 14 is arranged on the firstrotatable member 11 side of the thrust bearing 14. As shown as anexample in FIG. 3 , the detecting element 162 of the encoder 16 isarranged between the inner circumferential wall of the washer 141 andthe outer circumferential wall of the shaft member 13. Specifically, thedetecting element 162 is attached to the bottom face of the recessportion 115 of the first rotatable member 11 that faces the scale 161 inthe axial direction.

The scale 161 is concentric with the shaft member 13, and has a surfaceprovided with divisions on which the optical reflectance periodicallychanges in the circumferential direction. It is possible to detect arelative rotational angle between the adjacent rotatable members (11 and12), by reading the divisions using the detecting element 162. That isto say, the detecting element 162 is configured as appropriate to becapable of emitting light to the scale 161 and receiving light reflectedfrom the scale 161.

The detecting element 162 outputs an electrical signal according to thereceived reflected light via a wiring board 163 to the outside. Thewiring board 163 is constituted, for example, by a flexible printedcircuit (FPC). The wiring board 163 is formed in an L-shape, and has astraight-line portion and a projecting portion 164 projecting from thestraight-line portion. As shown as an example in FIG. 3 , the end faceof the projecting portion 164 is provided with a connector portion 165.

Furthermore, as shown as an example in FIGS. 1 and 3 , the firstrotatable member 11 is provided with a wiring groove portion 114 with ashape that conforms to the shape of the wiring board 163 such that thewiring board 163 can be extended from the internal space to the outside.The wiring groove portion 114 linearly extends from the second faceportion 112 including the recess portion 115 to the side wall portion113, and has substantially the same length as the straight-line portionof the wiring board 163. Moreover, the portion of the wiring grooveportion 114 positioned at the side wall portion 113 is adjacent to thecoupling portion 21.

Thus, as indicated by the arrows in FIG. 3 , when the straight-lineportion of the wiring board 163 is positioned along the wiring grooveportion 114, and the projecting portion 164 is bent toward the couplingportion 21, the projecting portion 164 can be arranged at a bottomportion 214 of the groove portion 211 of the coupling portion 21.Accordingly, in the present embodiment, the projecting portion 164 ofthe wiring board 163 is bonded to the bottom portion 214. That is tosay, the connector portion 165 of the wiring board 163 is arrangedinside the groove portion 211 of the coupling portion 21.

Accordingly, in the present embodiment, a cable 17 extending from anapparatus that uses data of the rotational angle detected by thedetecting element 162 (e.g., a control apparatus for controlling anactuator) can be arranged along groove portions 314 of the link member31 so as to be coupled with the wiring board 163. That is to say, asshown as an example in FIG. 3 , in a state where a cord portion of thecable 17 is fitted into the groove portion 314 of the link member 31, aconnector portion 171 of the cable 17 can be coupled with the connectorportion 165 of the wiring board 163 in the groove portion 211 of thecoupling portion 21.

With this configuration, the encoder 16 can detect a relative rotationalangle between the adjacent rotatable members (11 and 12). That is tosay, since the plate 142 is positioned by causing the projecting portion128 of the second rotatable member 12 to be fitted into the hole portion143, when the second rotatable member 12 axially rotates, the scale 161axially rotates by the same angle as the axial rotation of the secondrotatable member 12. In a similar manner, since the detecting element162 is attached to the bottom face of the recess portion 115, when thefirst rotatable member 11 axially rotates, the detecting element 162axially rotates by the same angle as the axial rotation of the firstrotatable member 11. That is to say, the scale 161 and the detectingelement 162 relatively rotate axially by the angle of the relativerotation between the first rotatable member 11 and the second rotatablemember 12. The end face of the scale 161 is provided with divisions onwhich the optical reflectance periodically changes in thecircumferential direction, and the detecting element 162 can read thedivisions (reflected light). Thus, it is possible to specify a relativerotational angle between the adjacent rotatable members (11 and 12),from the output (an electrical signal according to reflected light) ofthe detecting element 162.

Coupling Portion

Next, the method for coupling the link member 31 with the couplingportion 21 will be described with reference to FIGS. 4, 5A, 5B, and 6 aswell. FIG. 4 is a partially enlarged view schematically showing anexample of the coupling portion 21 of the joint structure 1 according tothe present embodiment. FIG. 5A is a cross-sectional view schematicallyshowing an example of a state before the link member 31 is coupled withthe coupling portion 21. FIG. 5B is a cross-sectional view schematicallyshowing an example of a state after the link member 31 is coupled withthe coupling portion 21. FIG. 6 schematically shows an example of acoupling state between an end face 210 of the coupling portion 21 and anend face 310 of the link member 31.

As shown as an example in FIGS. 1 and 4 , the coupling portions 21according to the present embodiment each have a shape obtained bycutting, in the tangential direction, an arc portion of the side wallportion (113 or 123) of the rotatable member. Specifically, the couplingportions 21 of the rotatable members (11 and 12) each have an end face210 that is flat and perpendicular to the radial direction, and thegroove portion 211 is formed inward in the radial direction from the endface 210. The groove portion 211 extends through a tangential directionthat is perpendicular to the radial direction, and thick-wall portions212 projecting inward are respectively provided at the upper ends of apair of groove walls of the groove portion 211. Accordingly, the grooveportion 211 is formed to have a substantially inverted T-shapedcross-section. Note that the end face 210 is provided with fourrectangular protruding portions 213 projecting outward in the radialdirection.

Meanwhile, as shown as an example in FIGS. 1 and 6 , the link member 31according to the present embodiment is provided with the groove portions314 that are respectively along both side face portions in thelongitudinal direction. Accordingly, the link member 31 is formed tohave a substantially H-shaped cross-section. Since edge portions 315 ofa pair of groove walls constituting each groove portion 314 both projectinward, the groove portion 314 is formed to have a substantiallyinverted T-shaped cross-section. Furthermore, as shown as an example inFIGS. 5A and 5B, the link member 31 has, at the center on its flat endface 310, a hole portion 311 extending in the longitudinal directionfrom the end face 310. The link member 31 is a frame member made of, forexample, a metal such as aluminum or titanium or a resin such asengineering plastic. However, the material of the link member 31 doesnot have to be limited to these, and may be selected as appropriateaccording to an embodiment.

In the present embodiment, as shown as an example in FIGS. 5A and 5B,the coupling portion 21 and the link member 31 are coupled to each othervia the wedge member 32 as follows. That is to say, the wedge member 32includes a rectangular head portion 321 with substantially the same sizeas the wide-width portion of the groove portion 211 of the couplingportion 21, and a rectangular body portion 322 with substantially thesame size as the narrow-width portion of the groove portion 211.Accordingly, the wedge member 32 is formed to have a substantiallyT-shaped cross-section.

The wedge member 32 is arranged such that the head portion 321 is fittedinto the groove portion 211 of the coupling portion 21. Accordingly, asshown as an example in FIG. 5A, the wedge member 32 is interlocked withthe thick-wall portions 212 of the groove portion 211 of the headportion 321, and the body portion 322 project out of the groove portion211. The portion projecting out of the groove portion 211 of the bodyportion 322 is provided with a through hole 323 in the shape of a columnwith a diameter that is slightly larger than the diameter of a malethread portion 333 of a screw 33 such that the screw 33 can be insertedthereinto. Furthermore, the side of the through hole 323 for receivingthe screw 33 is provided with a tapered portion 324 that conforms to atapered portion 332 of the screw 33.

In conformity with the through hole 323, the link member 31 is providedwith a through hole 312 that extends in the width direction (theupper-lower direction in FIGS. 5A and 5B) from the upper face in thedrawings to the hole portion 311, and a through hole 313 that extends inthe width direction from the hole portion 311 to the lower face in thedrawings. In the present embodiment, the through hole 312 has a diameterthat is substantially the same as the outer diameter of a head portion331 of the screw 33, in order to allow the screw 33 to be inserted fromthe through hole 312 side. Furthermore, the through hole 313 has adiameter that is substantially the same as the outer diameter of themale thread portion 333 of the screw 33, and the inner circumferentialwall thereof is provided with a female thread into which the male threadportion 333 is to be screwed. Accordingly, as shown as an example inFIG. 5B, the coupling portion 21 and the link members 31 can be coupledwith each other, by fitting the head portion 321 of the wedge member 32into the groove portion 211 of the coupling portion 21, inserting thebody portion 322 into the hole portion 311 of the link member 31, andfastening the screw 33.

Here, a distance WA from the end face 210 of the coupling portion 21 tothe through hole 323 in a state where the head portion 321 of the wedgemember 32 is fitted into the groove portion 211 is slightly shorter thana distance WB from the end face 310 of the link member 31 to the throughhole 313 into which the male thread portion 333 of the screw 33 isscrewed. Thus, when screwing the male thread portion 333 of the screw 33into the through hole 313, the tapered portion 332 of the screw 33 comesinto contact with the tapered portion 324 of through hole 323 of thewedge member 32 and pulls the wedge member 32 toward the link member 31.

Accordingly, the wedge member 32 is tensioned in the radial direction(the left-right direction in the drawing), and, due to this tension, thecoupling portion 21 and the link member 31 are firmly coupled with eachother. Specifically, the coupling portion 21 and the link member 31 arecoupled with each other in the radial direction due to a force that actsfrom the head portion 321 of the wedge member 32 to the thick-wallportions 212 of the coupling portion 21 and a force that acts from thescrew 33 via the through hole 323 of the wedge member 32 to the innercircumferential walls of the through holes (312 and 312) of the linkmember 31. At this time, the link member 31 is coupled with the couplingportion 21 such that the link member 31 extends along the radialdirection of the rotatable members (11 and 12), that is, such that theradial direction of the rotatable members (11 and 12) matches thelongitudinal direction of the link member 31. In the present embodiment,the link member 31 can be coupled with the coupling portion 21 of eachof the rotatable members (11 and 12) through such simple fastening usingthe wedge member 32 and the screw 33.

However, in the present embodiment, since the groove portion 211 of thecoupling portion 21 extends throughout a tangential direction (directionthat is perpendicular to the section of the diagram in FIGS. 5A and 5B)that is perpendicular to the radial direction, the wedge member 32 maymove in the tangential direction, and the head portion 321 may bedetached from the groove portion 211 in the tangential direction. Thus,in the present embodiment, the end face 210 of the coupling portion 21is provided with the four protruding portions 213.

Specifically, as shown as an example in FIG. 6 , the four protrudingportions 213 are arranged at four corners of a rectangle so as to beinterlocked with the edge portions 315 of the link member 31.Accordingly, in a state where the coupling portion 21 and the linkmember 31 are coupled with each other, the edge portions 315 of the linkmember 31 are interlocked with the protruding portions 213, and thusmovement in the tangential direction (the upper-lower direction in FIG.6 ) of the wedge member 32 for coupling the coupling portion 21 and thelink members 31 can be suppressed. Furthermore, the protruding portions213 are in contact with the link member 31 also in the axial direction,wobbling of the link member 31 in the axial direction can be suppressed.Furthermore, in the present embodiment, the protruding portions 213conform to the shape near the edge portions 315 of the link member 31,and thus the protruding portions 213 can be used for positioning of thelink member 31.

As shown as an example in FIGS. 2, 5A, and 5B, the thickness of each ofthe rotatable members (11 and 12) according to the present embodiment,in other words, the height of each of the side wall portions (113 and123) is the same as the thickness (the length in the left-rightdirection in FIG. 2 ) of each of the link members 31. Accordingly, whenthe rotatable members (11 and 12) rotate, the link members 31 coupledwith the rotatable members (11 and 12) do not interfere with each other.Note that “the same” refers not only to a state in which the thicknessof each of the rotatable members (11 and 12) is completely the same asthe thickness of each of the link members 31 but also to a state inwhich the thickness of each of the rotatable members (11 and 12) islarger than the thickness of each of the link members 31 to the extentthat they do not interfere with each other or later-describedreinforcing plates 51 can be arranged.

§ 2 Usage Example

Various link mechanisms can be constructed using the joint structure 1according to the present embodiment. Hereinafter, three examples areshown.

Scott Russell Mechanism

First, an example of constructing a robot 400 having parallel-linkedScott Russell mechanism using six joint structures 408 a to 408 f willbe described with reference to FIGS. 7A and 7B. FIGS. 7A and 7B are aperspective view and a side view schematically showing an example of therobot 400 according to this usage example. Note that the jointstructures are denoted by reference numerals 408 a to 408 f merely forthe sake of ease of description, and the joint structures 408 a to 408 fcorrespond to the joint structure 1 described above. The jointstructures 408 a to 408 f are arranged such that the second rotatablemember is on the front side in the section of the diagrams. In a similarmanner, the link members are denoted by reference numerals 407 a to 407h merely for the sake of ease of description, and the link members 407 ato 407 h correspond to the link members 31 described above.

The robot 400 according to this usage example includes a rectangularbase 401 that is placed on the ground, and a support 402 in the shape ofa rectangular column extending in the vertical direction from the upperface of the base 401. A pair of actuators (403 and 404) are attached tothe support 402 so as to be spaced from each other in the upper-lowerdirection. Furthermore, two movable portions (405 and 406) are attachedso as to be movable (slidable) in the upper-lower direction between thepair of actuators (403 and 404).

The actuators (403 and 404) drive output rods in the vertical direction,thereby moving the movable portions (405 and 406) in the upper-lowerdirection. Specifically, the actuator 403 arranged on the upper sidemoves the movable portion 405 in the upper-lower direction, and theactuator 404 arranged on the lower side moves the movable portion 406 inthe upper-lower direction. That is to say, the movable portions (405 and406) can move in the upper-lower direction independently of each other.

Note that the type of the actuators (403 and 404) may be selected asappropriate according to an embodiment as long as the output rods can bemoved in the vertical direction. For example, linear actuators, electricactuators, hydraulic actuators, pneumatic actuators, hybrid actuators,or the like may be used as the actuators (403 and 404). Furthermore, thetype of the movable portions (405 and 406) may be selected asappropriate according to an embodiment as long as they can move in theupper-lower direction. For example, linear bearings may be used as themovable portions (405 and 406).

A link member 407 a extending in the horizontal direction is attached tothe movable portion 405. In a similar manner, two link members (407 band 407 c) extending in the horizontal direction are attached to themovable portion 406 so as to be spaced from each other in theupper-lower direction. The link members 407 a to 407 c are formed asshort members.

A joint structure 408 a is attached to the end portion of the linkmember 407 a on the side opposite to the movable portion 405.Specifically, the link member 407 a is coupled with a coupling portionof the first rotatable member of the joint structure 408 a. Furthermore,a link member 407 d that is longer in the longitudinal direction thanthe link member 407 a is coupled with a coupling portion of the secondrotatable member of the joint structure 408 a.

Meanwhile, the end portion of the link member 407 b on the side oppositeto the movable portion 406 is coupled with a coupling portion of thesecond rotatable member of the joint structure 408 b. Furthermore, alink member 407 e that is longer in the longitudinal direction than thelink member 407 b is coupled with a coupling portion of the firstrotatable member of the joint structure 408 b.

The link members (407 d and 407 e) are coupled with a joint structure408 d. Specifically, the link member 407 e is coupled with a couplingportion of the first rotatable member of the joint structure 408 d, andthe link member 407 d is coupled with a coupling portion of the secondrotatable member. Furthermore, a link member 407 g with a length similarto that of the link member 407 e is coupled with another couplingportion of the first rotatable member of the joint structure 408 d.

Accordingly, the Scott Russell mechanism is constituted by the threejoint structures (408 a, 408 b, and 408 d) and the five link members(407 a, 407 b, 407 d, 407 e, and 407 g). The end portion of the linkmember 407 g on the side opposite to the joint structure 408 d iscoupled with a coupling portion of the first rotatable member of a jointstructure 408 e. Furthermore, a link member 407 h with a length that isthe same as the distance in the upper-lower direction between the twojoint structures (408 b and 408 c) adjacent to the movable portion 406is coupled with a coupling portion of the second rotatable member of thejoint structure 408 e. The end portion of the link member 407 h on theside opposite to the joint structure 408 e is coupled with a couplingportion of the second rotatable member of the joint structure 408 f. Afront end portion 409 such as an end effector is attached to the linkmember 407 h.

Meanwhile, the end portion of the link member 407 c arranged below thelink member 407 b, on the side opposite to the movable portion 406, iscoupled with a coupling portion of the second rotatable member of thejoint structure 408 c. Furthermore, a link member 407 f with a lengththat is the same as the total length of the two link members (407 e and407 g) and the joint structure 408 d arranged above is coupled with acoupling portion of the first rotatable member of the joint structure408 c. The end portion of the link member 407 f on the side opposite tothe joint structure 408 c is coupled with a coupling portion of thefirst rotatable member of the joint structure 408 f.

That is to say, in the robot 400, the pair of link members (407 e and407 g) are parallel to the link member 407 f, the links connecting thefour joint structures (408 b, 408 c, 408 f, and 408 e) form aparallelogram (parallel link). Thus, due to the characteristics of theScott Russell mechanism, the robot 400 can move the front end portion409 in the upper-lower and front-rear directions (the arrow directionsin FIG. 7B), by driving the actuators (403 and 404) and moving themovable portions (405 and 406) in the upper-lower direction. Moreover,due to the characteristics of the parallel link, the robot 400 can keepthe front end portion 409 horizontal even when driving the actuators(403 and 404) and moving the front end portion 409 attached to the linkmember 407 h in the upper-lower and front-rear directions.

Note that, in the robot 400, two coupling portions of the same rotatablemember are simultaneously used only in the joint structure 408 d. Thatis to say, two coupling portions of the first rotatable member of thejoint structure 408 d are used to linearly couple the two link members(407 e and 408 g). On the other hand, only one coupling portion is usedto couple the link members in the rotatable members of the other jointstructures. Thus, it is sufficient that the rotatable members of theother joint structures each have at least one coupling portion, and theother coupling portions may be omitted. Furthermore, the rotatablemembers that are coupled by the link members do not have to be limitedto the examples described above, and may be selected as appropriateaccording to an embodiment.

As described above, if two or more coupling portions are provided on aside wall portion of at least one rotatable member, the robot 400 havingparallel-linked Scott Russell mechanism can be constructed. Thus, it ispossible to realize a complex link mechanism such as a parallel-linkedScott Russell mechanism as described above by arranging a plurality ofcoupling portions on a side wall portion of at least one rotatablemember among the plurality of rotatable members.

Wire Driving Mechanism

Next, an example of driving the joint structure 1 by wires using thewire-driving groove portions 129 will be described with reference toFIG. 8 . FIG. 8 is a perspective view schematically showing an exampleof a robot 410 having three joint structures 412 that are driven bypulling wires. As in the foregoing example, the joint structures aredenoted by reference numerals 412A and 412B merely for the sake of easeof description, and the joint structures (412A and 412B) correspond tothe joint structure 1 described above. Specifically, the joint structureusing the first rotatable member 11 on the front side in the section ofthe diagram is denoted by “412A”, and the joint structure using thesecond rotatable member 12 on the front side in the section of thediagram is denoted by “412B”. Hereinafter, they will be simply referredto as “joint structures 412” if they are not to be distinguished fromeach other. In a similar manner, the link members are denoted by areference numeral 411 merely for the sake of ease of description, andthe link members 411 correspond to the link members 31 described above.

In the robot 410 according to this usage example, four link members 411are coupled by the three joint structures 412. The link members 411 areas appropriate coupled with coupling portions of the joint structures412. Specifically, the first rotatable member of the joint structure412B and the second rotatable member of the joint structure 412Aarranged below the joint structure 412B are coupled with each other viathe link member 411. Furthermore, the second rotatable member of thejoint structure 412B and the first rotatable member of the jointstructure 412A arranged above the joint structure 412B are coupled witheach other via the link member 411. Above each of the joint structures412, a pair of fixtures (413 and 414) are fixed to the groove portionsof the link member 411.

End portions of the wires (415 and 416) are fixed to the fixtures (413and 414). Specifically, an end portion of the wire 415 is fixed to thefixture 413 and an end portion of the wire 416 is fixed to the fixture414. The wires (415 and 416) are Bowden cables that are arranged alongthe wire-driving groove portions 129 and are then allowed to passthrough binding members 417 arranged below the respective jointstructures 412 so as to be coupled with a drive source provided outside.The drive source is, for example, a pneumatic actuator, a motor, or thelike.

The thus configured robot 410 according to this usage example operatesas follows. That is to say, when the wire 415 is pulled by the externaldrive source, the force acts on the fixture 413, and the link member 411above the joint structure 412 that is to be driven is pulled in thearrow A1 direction. Accordingly, the rotatable member coupled with thelink member 411 rotates. In a similar manner, when the wire 416 ispulled by the external drive source, the force acts on the fixture 414,and the link member 411 above the joint structure 412 that is to bedriven is pulled in the arrow A2 direction. Accordingly, the rotatablemember coupled with the link member 411 rotates. The robot 410 accordingto this usage example can drive the joint structures 412 by pullingwires in this manner.

In this usage example, each joint structure 412A is used in a state ofbeing reversed about an axis perpendicular to the axial direction withrespect to the joint structure 412B. The first rotatable member of thejoint structure 412B and the second rotatable member of the jointstructure 412A arranged below the joint structure 412B are coupled witheach other via the link member 411. The second rotatable member of thejoint structure 412B and the first rotatable member of the jointstructure 412A arranged above the joint structure 412B are coupled witheach other via the link member 411. Accordingly, two joint structures(412A and 412B) adjacent to each other via the link member 411 arearranged such that the rotatable members face each other in thedirection that is perpendicular to the axial direction. Thus, the robot410 according to this usage example is compact in the axial direction.However, the use state of the joint structures for making the linkmechanism compact in the axial direction is not limited to the foregoingexample. For example, as in the robot 400 described above, adjacent twojoint structures may be used in a state of being oriented in the samedirection. In this case, the radial bearings may be transition-fittedwith slight gap provided at the shaft members and the inner walls of thethrough holes instead of being interference-fitted to any of the shaftmembers and the inner walls of the through holes. With thisconfiguration, since adjacent two joint structures are used in a stateof being oriented in the same direction, fasteners and the like can bearranged in one direction. Accordingly, it is possible to construct alink mechanism in which the joint structures can be subjected tomaintenance operations from one direction even when grease up ofbearings or adjustment of pressurization is needed.

Delta Robot

Next, an example of constructing a delta robot 420 having parallel linkmechanisms at three points through 18 joint structures 424 will bedescribed with reference to FIG. 9A. FIG. 9A is a perspective viewschematically showing an example of the delta robot 420 according tothis usage example. As in the foregoing example, the joint structuresdenoted by a reference numeral 424 merely for the sake of ease ofdescription, and the joint structures 424 correspond to the jointstructure 1 described above.

The delta robot 420 according to this usage example has a base portion421 in the shape of a triangular frame. A rotary motor 422 is attachedto the center of each side of the base portion 421, and the rotary motor422 is coupled with a link member 423 a. The link member 423 acorresponds to the link member 31 described above.

The joint structure 424 is coupled with the other end portion of thelink member 423 a. A T-shaped link member 423 b is coupled with thejoint structure 424. A parallel link is constituted by the link member423 b together with four joint structures 424, two link members (423 cand 423 d) with the same length, and a T-shaped link member 423 e.

The link members (423 c and 423 d) correspond to the link members 31described above. Furthermore, the end portions of the T-shaped linkmembers (423 b and 423 e) have a configuration similar to that of theend portions of the link members 31. The T-shaped link members (423 band 423 e) can be each produced, for example, by welding or bonding twolink members 31 as appropriate. The link members 423 a to 423 e arecoupled with the coupling portions of the joint structures 424 asappropriate.

Furthermore, the remaining end portion of the T-shaped link member 423 eis also coupled with joint structures 424, and a front end portion 425in the shape of a triangular frame is attached to the three jointstructures 424 in total arranged lowermost. Specifically, the corners ofthe front end portion 425 are respectively provided with link portions426 with a configuration similar to that of the end portions of the linkmembers 31, and the front end portion 425 are coupled with the jointstructures 424 respectively via the link portions 426.

The thus configured delta robot 420 according to this usage exampleoperates as follows. That is to say, in the delta robot 420 according tothis usage example, parallel link mechanisms are respectively coupledwith the three rotary motors 422 arranged at the base portion 421. Thus,if all or a part of the three rotary motors 422 are driven, the parallellink mechanisms coupled with the driven rotary motors 422 can be movedin the upper-lower direction, and thus it is possible to move the frontend portion 425 in each direction while maintaining the horizontalposture.

As shown as an example in FIG. 9B, the actuators used for the deltarobot 420 do not have to be limited to the rotary motors 422. FIG. 9B isa perspective view schematically showing an example of a delta robot420A in which linear motors 427 that drive output rods in the verticaldirection are used as actuators.

As shown as an example in FIG. 9B, the delta robot 420A according tothis usage example has the same configuration as that of the delta robot420 described above, except that the rotary motors 422 are replaced bythe linear motors 427 for linear movement. The delta robot 420A canoperate in a manner similar to that of the delta robot 420 by moving theoutput rods of the linear motors 427 in the upper-lower direction.

Characteristics

As described above, in the joint structure 1 according to the presentembodiment, the two rotatable members (11 and 12) are coupled with eachother in an axially rotatable manner. Moreover, each of the rotatablemembers (11 and 12) includes two coupling portions 21 for coupling thelink members 31 constituting a link of a robot. Thus, as shown in theforegoing usage example, it is possible to couple the plurality of linkmembers 31 via the joint structures 1, by coupling the different linkmembers 31 with the different rotatable members (11 and 12).Furthermore, when the link members 31 are moved by an external forceacting from actuators or the like, the rotatable members (11 and 12) canaxially rotate in accordance with the rotation of the link members 31.

That is to say, the joint structures 1 according to the presentembodiment can be driven by an external force transmitted from the linkmembers 31, and thus it is possible to change a positional relationshipbetween the link members 31 coupled with the different rotatable members(11 and 12). Moreover, it is possible to construct various linkmechanisms as described in the usage examples using the joint structures1. Accordingly, the joint structures 1 according to the presentembodiment are modularized and can be used for general purposes.

Furthermore, in the present embodiment, the face portions (112 and 121)that face each other, of the rotatable members (11 and 12) that areadjacent to each other in the axial direction, are respectively providedwith the recess portions (115 and 126), and the thrust bearing 14 isarranged in the internal space defined by the recess portions (115 and126). Thus, the strength in the axial direction of the joint structure 1according to the present embodiment is ensured by the thrust bearing 14.

Furthermore, in the present embodiment, the internal space defined bythe recess portions (115 and 126) further accommodates the encoder 16capable of detecting a relative rotational angle between the rotatablemembers (11 and 12). Thus, in the present embodiment, the encoder 16 canbe prevented from being coming into contact with the outside withoutusing extra constituent elements such as casings, and thus thepossibility that the encoder 16 will be out of order due to an externalforce can be significantly lowered.

Furthermore, since the encoder 16 is arranged in the internal space, itis less likely to be affected by the deformation of the joint structure1 compared with the case in which it is arranged outside. That is tosay, even when the outer shape of the joint structure 1 is deformed byan external force, the internal space defined by the recess portions(115 and 126) is less likely to be deformed. Thus, even when the outershape of the joint structure 1 is deformed, a positional relationshipbetween the scale 161 and the detecting element 162 constituting theencoder 16 hardly changes. Accordingly, even when used in a situationwhere an external force is applied, the joint structure 1 can stablydetect a relative rotational angle between the rotatable members (11 and12).

Moreover, in the present embodiment, the scale 161 rotates in one piecewith the second rotatable member 12, and the detecting element 162rotates in one piece with the first rotatable member 11. Thus, in thejoint structure 1 according to the present embodiment, errors are notcaused by backlash or slippage compared with a method in which rotationof the rotatable members (11 and 12) is measured using an externalencoder via transmission components such as belts, gears, or couplings.Accordingly, the joint structure 1 according to the present embodimentcan accurately detect a relative rotational angle between the rotatablemembers (11 and 12).

In the present embodiment, the rotatable members (11 and 12) each have acolumnar basic shape, and the coupling portions 21 are formed bycutting, in the tangential direction, an arc portion of the basic shape.That is to say, the rotatable members (11 and 12) do not have a shapehaving a portion projecting from a circle, and thus the rotatablemembers (11 and 12) can be produced through lathe machining. Thus, evenwhen producing the rotatable members (11 and 12) through processing, itis very easy to produce the rotatable members (11 and 12).

Furthermore, the joint structure 1 according to the present embodimentis of an externally-driven type, and constituent components that areessential for a joint structure with a built-in actuator, such as ahousing for accommodating the actuator, are not necessary. Thus, thejoint structure 1 can be made compact and light. Moreover, the jointstructure 1 according to the present embodiment does not have a complexstructure, and thus it can be easily produced with a simple design.

Furthermore, in the joint structure 1 according to the presentembodiment, the first rotatable member 11 excluding the shaft member 13has substantially the same shape as the second rotatable member, andthus the rotatable members (11 and 12) are bilaterally symmetric aboutthe axial direction. Specifically, the side face portions (113 and 123)have a shape that is symmetric about a plane perpendicular to the axialdirection of the shaft member 13. Thus, with the joint structure 1according to the present embodiment, it is easy to construct a closedlink mechanism. Furthermore, if the rotatable members (11 and 12) of theplurality of joint structures 1 are alternately coupled via the linkmembers 31, it is possible to construct a link mechanism withoutincreasing the volume.

Furthermore, in the present embodiment, the two coupling portions 21provided in each of the rotatable members (11 and 12) are arranged atpositions at 180 degrees about an axis, on the side wall portions (113and 123). Accordingly, the coupling portions 21 of each of the rotatablemembers (11 and 12) are arranged symmetric about the axial direction,and thus the link members 31 coupled with the rotatable members (11 and12) can be used symmetrically about the axial direction. For example,even when a link mechanism including the joint structure 1 in which thelink member 31 on the first rotatable member 11 side is fixed is changedby reversing the joint structure 1 so that the link member 31 on thesecond rotatable member 12 side is fixed, the same link mechanism can beconstructed. Furthermore, in the present embodiment, the rotatablemember 11, which is one of the two rotatable members (11 and 12), isformed in one piece with the shaft member 13, and the rotatable member12, which is the other rotatable member, has the through hole 124 intowhich the shaft member 13 can be inserted. Then, the radial bearings 15can be arranged so as to be interference-fitted to the shaft member 13and clearance-fitted to the inner circumferential wall of the throughhole 124, or so as to be clearance-fitted to the shaft member 13 andclearance-fitted to the inner circumferential wall of the through hole124. Accordingly, for example, the following effects can be expected.That is to say, in the joint structure 1 according to the presentembodiment, when the link member 31 on the first rotatable member 11side is fixed, the second rotatable member 12 rotates, and radial loadsof the rotating outer ring and the stationary inner ring act inside.Thus, the diameter of the through hole 124 into which the radialbearings 15 are to be inserted is determined assuming the radial loads.For example, if the second rotatable member 12 is driven at unbalancedload, the fitting of the radial bearings 15 is set such that the innerring is interference-fitted and the outer ring is clearance-fitted. Thatis to say, the radial bearings 15 with an inner diameter that isslightly smaller than the outer diameter of the shaft member 13 and anouter diameter that is slightly smaller than the diameter of the throughhole 124 are arranged so as to be interference-fitted to the shaftmember 13 and clearance-fitted to the inner circumferential wall of thethrough hole 124. Thus, the diameter of the through hole 124 isdetermined so as to be larger than the outer diameter of the radialbearings 15. Meanwhile, when the second rotatable member 12 is driven ata stationary load, setting of the radial bearings 15 needs to be changedsuch that the inner ring is clearance-fitted and the outer ring isinterference-fitted. That is to say, the radial bearings 15 with aninner diameter that is slightly larger than the outer diameter of theshaft member 13 and an outer diameter that is slightly larger than thediameter of the through hole 124 are arranged so as to beclearance-fitted to the shaft member 13 and interference-fitted to theinner circumferential wall of the through hole 124. At this time, if theradial bearings 15 are not changed, the diameter of the through hole 124needs to be changed. On the other hand, the joint structure 1 accordingto the present embodiment has a shape that allows the link members 31 tobe used in a bilaterally symmetric manner.

Thus, if the link member 31 on the second rotatable member 12 side isfixed and a stationary load is caused to act on the first rotatablemember 11, the joint structure 1 according to the present embodiment canbe used as it is for link mechanisms without changing the diameter ofthe through hole 124 or the diameter of the shaft member 13, even whenload conditions applied thereto vary. If a link mechanism is constructedusing a plurality of joint structures 1, the joint structures 1 in bothforms in which the inner rings of the radial bearings 15 areinterference-fitted and in which the inner rings of the radial bearings15 are clearance-fitted may be used. In this case, it is possible toconstruct a link mechanism that is compact in the axial direction, byusing, symmetrically about the axial direction, the joint structure 1 inwhich the inner rings of the radial bearings 15 are interference-fittedand the joint structure 1 in which the inner rings of the radialbearings 15 are clearance-fitted.

Here, “the coupling portions are arranged symmetric about the axialdirection” refers to a state in which the connecting relationship of therotatable members (11 and 12) can be switched by reversing the jointstructure 1 about an axis (an axis SA or an axis SB in FIG. 1 )perpendicular to the axial direction, while maintaining the positionalrelationship between the plurality of link members 31 coupled with therotatable members (11 and 12). That is to say, if it is assumed that thejoint structure 1 given as an example in FIG. 1 is reversed about theaxis SA (y axis) or the axis SB (z axis), the link member 31 coupledwith the first rotatable member 11 before reversing can be coupled withthe coupling portion 21 of the second rotatable member 12 withoutchanging the position after reversing. Furthermore, the link member 31coupled with the second rotatable member 12 before reversing can becoupled with the coupling portion 21 of the first rotatable member 11without changing the position after reversing. Accordingly, it ispossible to use the joint structure 1 as a joint of inner ring rotationin which the first rotatable member 11 rotates or as a joint of outerring rotation in which the second rotatable member 12 rotates, bychanging the orientation of the joint structure 1 that is used for thelink mechanism, without changing the structure of the link mechanism.Furthermore, it is also possible to change the positions of the wiringgroove portions 114 as appropriate. Note that “the coupling portions arearranged symmetric about the axial direction” is not limited to theexample in which two coupling portions provided in each of the rotatablemembers (11 and 12) are arranged at positions at 180 degrees about anaxis, but may be designed as appropriate according to an embodiment.

Furthermore, the two coupling portions 21 provided on each of the sidewall portions (113 and 123) of the rotatable members (11 and 12) arearranged at positions at 180 degrees about an axis, and thus thecoupling portions 21 are symmetric about an axis in each of therotatable members (11 and 12). Thus, even when the joint structure 1according to the present embodiment is axially rotated, it can be usedwhile maintaining the positional relationship between the link members.Accordingly, it is also possible to change the positions of the wiringgroove portions 114 as appropriate. Note that the state in which thecoupling portions are symmetric about an axis in each rotatable memberis not limited to the example in which two coupling portions arearranged at positions at 180 degrees about an axis, and may be designedas appropriate according to an embodiment.

Moreover, in the joint structure 1 according to the present embodiment,it is also possible to make not only the outer shape but also the entireweight balance bilaterally symmetric, by selecting as appropriate theweights of the constituent elements. Thus, the following effects can beexpected. That is to say, since a conventional joint structure with abuilt-in actuator is driven by an electric motor, use of an electricmotor alone leads to driving at high speed and low torque, which is notsuitable to drive a robot. Thus, an electric motor is used incombination with a reduction drive.

Accordingly, the conventional joint structure with a built-in actuatorcannot make the entire weight balance bilaterally symmetric due to adifference between the flow rates of the electric motor and thereduction drive. Thus, in a link mechanism using such a joint structure,typically, the weights on the left and right sides cannot be balanced.Accordingly, a force that twists the links occurs, and thus the linksbefore and after the joint structure may come into contact with eachother. This aspect is problematic especially in the case of robots suchas the robot 400 in which the link mechanisms are arranged in a verticalface.

Furthermore, for example, it is assumed that joint structures whoseweight balance is not bilaterally symmetric are alternatively arrangedto make the weight balance of the entire link mechanism bilaterallysymmetric. Also in this case, since the joint structures arealternatively arranged, wires extending from the joint structures becomealternatively located, and thus the arrangement of wires in the entirelink mechanism becomes poor.

Meanwhile, the joint structure 1 according to the present embodiment isof an externally-driven type, and does not have a built-in electricmotor and reduction drive, and thus it is possible to make the entireweight balance bilaterally symmetric, by selecting as appropriate theweights of the constituent elements. Thus, in the link mechanism (e.g.,the robot 400 described above) using the joint structure 1, the entireweight balance can be made substantially bilaterally symmetric, and thelink members 31 before and after the joint structure 1 can be preventedfrom coming into contact with each other. Moreover, the joint structures1 do not have to be alternatively arranged in order to make the weightbalance of the link mechanism bilaterally symmetric, and thus thearrangement of wires in the entire link mechanism can be prevented frombecoming poor.

§ 3 Modified Example

Above, an embodiment of the present invention was described in detail,but the description above is in all aspects merely an example of thepresent invention. It will be appreciated that various improvements andmodifications can be made without departing from the scope of thepresent invention. Furthermore, the constituent elements of the jointstructure 1 may be omitted, replaced or added, as appropriate, accordingto an embodiment. The shape and the size of the constituent elements ofthe joint structure 1 may be set as appropriate according to anembodiment. For example, the following changes may be made. Note that inmodified examples described below, the same constituent elements as inthe foregoing embodiment are denoted by the same reference numerals, anda description thereof has been omitted as appropriate. The followingmodified example may be combined as appropriate.

3.1

For example, the joint structure 1 according to the foregoing embodimentincludes two rotatable members (11 and 12). However, the number ofrotatable members included in the joint structure of the presentinvention does not have to be that in the examples of the foregoingembodiment, and may be three or more.

Hereinafter, an example thereof will be described with reference to FIG.10 . FIG. 10 is a cross-sectional view schematically showing an exampleof a joint structure 1A including three rotatable members (11, 12, and18). As shown in FIG. 10 , the joint structure 1A according to thismodified example is formed so as to be substantially similar to in thejoint structure 1 described above. That is to say, a third rotatablemember 18 has the same configuration as that of the second rotatablemember 12. The internal space between the first rotatable member 11 andthe second rotatable member 12 and the internal space between the secondrotatable member 12 and the third rotatable member 18 accommodate thethrust bearing 14 and an encoder as appropriate as in the foregoingembodiment. Furthermore, a shaft member 13A has the same configurationas that of the shaft member 13 according to the foregoing embodiment,except that the length in the axial direction is made longer by thelength for allowing the third rotatable member 18 to be attached.Furthermore, two radial bearings 15 are arranged between the secondrotatable member 12 and the shaft member 13A and between the thirdrotatable member 18 and the shaft member 13A, as in the foregoingembodiment. Accordingly, the joint structure 1A includes three rotatablemembers (11, 12, and 18) coupled with each other in an axially rotatablemanner.

That is to say, in the foregoing embodiment, it is possible to adjustthe number of second rotatable members 12 that are attached to the shaftmember 13 by adjusting the length in the axial direction of the shaftmember as appropriate. Accordingly, a joint structure including three ormore rotatable members can be produced as appropriate. Note that themethod for producing a joint structure including three or more rotatablemembers is not limited to the example described above, and may beselected as appropriate according to an embodiment, as in modifiedexamples, which will be described later.

3.2

For example, in the foregoing embodiment, the face portions (111, 112,121, and 122) of the rotatable members (11 and 12) are formed in theshape of a circle. However, the shape of the rotatable members (11 and12) does not have to be limited to this example, and may be selected asappropriate according to an embodiment. For example, the shape of theface portions (111, 112, 121, and 122) of the rotatable members (11 and12) may be a polygon such as a hexagon, or may be an oval. In the caseof these shapes, the outer shape of the rotatable members (11 and 12)may be formed symmetric about the axial direction.

3.3

Furthermore, for example, in the foregoing embodiment, each of therotatable members (11 and 12) includes two coupling portions 21.However, the number of coupling portions 21 included in each of therotatable members (11 and 12) is not limited to two, and may be selectedas appropriate according to an embodiment. For example, the number ofcoupling portions 21 included in each of the rotatable members (11 and12) may be one, or may be three or more. At this time, the couplingportions 21 may be arranged at the side wall portions (113 and 123) asin the foregoing embodiment, or may be arranged at the face portions(111, 112, 121, and 122) as in the foregoing modified example.

3.4

Furthermore, for example, in the foregoing embodiment, the couplingportions 21 are arranged at the side wall portions (113 and 123) of therotatable members (11 and 12). However, the arrangement of the couplingportions 21 does not have to be limited to this example, and thecoupling portions 21 may be arranged at the face portions (111, 112,121, and 122) of the rotatable members (11 and 12).

Hereinafter, an example thereof will be described with reference to FIG.11 . FIG. 11 schematically shows an example of a joint structure 1B inwhich a first face portion 111B of a first rotatable member 11B has acoupling portion 21B. As shown as an example in FIG. 11B, the firstrotatable member 11B has the same configuration as that of the firstrotatable member 11 described above, except that the first face portion111B is provided with the coupling portion 21B. The coupling portion 21Bhas the same configuration as that of the coupling portion 21. Thus, itis possible to couple the link members 31 with the coupling portion 21B,using the above-described coupling method.

If at least one coupling portion is provided at one of a pair of faceportions of at least one of a plurality of rotatable members, and atleast one coupling portion is provided at a side wall portion of anotherrotatable member of the plurality of rotatable members as shown as anexample in FIG. 11 , the following effects can be expected. That is tosay, the link connecting direction can be changed between the couplingportion provided at the face portion (e.g., the coupling portion 21B ofthe first rotatable member 11B) and the coupling portion provided at theside wall portion (e.g., the coupling portion 21 of the second rotatablemember 12). Thus, the link connecting direction can be changed without aspecial structure, and thus the link mechanism that is to be constructedcan be made compact on the whole.

Note that the face portion at which a coupling portion can be providedis not limited to the first face portion of the first rotatable member.For example, a coupling portion may be provided on the second faceportion side of the second rotatable member. Furthermore, if a couplingportion is provided at a face portion of each rotatable member, thecoupling portion may be provided via an attachment or the like.

3.5

Furthermore, for example, in the foregoing embodiment, the two couplingportions 21 are arranged at positions at 180 degrees about the center inthe surface direction of the rotatable members (11 and 12) (hereinafter,this angle is referred to as “angle between adjacent couplingportions”). However, if a plurality of coupling portions 21 are providedat the side wall portions (113 and 123), the positional relationshipbetween the coupling portions 21 does not have to be limited to thisexample, and may be selected as appropriate according to an embodiment.

For example, the angle between adjacent coupling portions may be set atan obtuse angle or an acute angle. Furthermore, for example, if apolygonal link is constructed using link members, the angle betweenadjacent coupling portions may be set to be the same as the angle of onecorner of the polygon such that the joint structures can be arranged atthe respective corners. If the joint structures in which the anglebetween adjacent coupling portions is an obtuse angle are used, forexample, a boomerang-shaped parallel link mechanism as shown in FIG. 12can be constructed.

FIG. 12 is a perspective view schematically showing an example of arobot 400C using joint structures 1C in which an angle between adjacentcoupling portions is an obtuse angle. In the robot 400C given as anexample in FIG. 12 , the joint structure 408 d arranged at the middle inthe Scott Russell mechanism portion of the robot 400 described above isreplaced by a joint structure 1C in which the angle between adjacentcoupling portions is an obtuse angle.

Thus, two link members (407 e and 407 g) coupled with the jointstructure 1C constitute a link that is bent in a boomerang shape.Accordingly, in this modified example, the link member 407 f of therobot 400 is replaced by the joint structure 1C and two link members 31c.

Each link member 31 c has the same configuration as that of the linkmember 31, and has the same length as each of the link members (407 eand 407 g). Accordingly, the link constituted by the two link members 31c and the joint structure 1C has the same shape as the link constitutedby the two link members (407 e and 407 g) and the joint structure 1C.That is to say, a boomerang-shaped parallel link is formed.

As described above, if the joint structure 1C in which the angle betweenadjacent coupling portions is an obtuse angle is used, the robot 400C inwhich the parallel link is in a boomerang shape can be constructed. Notethat the link on the lower side may use link members with the same shapeas the boomerang-shaped link constituted by two link members (407 e and407 g) without using the joint structure 1C.

Furthermore, for example, in the foregoing embodiment and modifiedexamples, the link member 31 is coupled with a rotatable member so as toextend in the radial direction or the axial direction (direction that isperpendicular to a face). However, the orientation in which the linkmember 31 is coupled does not have to be limited to this example, andmay be selected as appropriate according to an embodiment. For example,the end face 210 of the coupling portion 21 (21B) may be at an anglewith respect to the radial direction (axial direction). Accordingly, thelink member 31 can be coupled with the coupling portion 21 (21B) so asto be inclined from the radial direction or the axial direction withrespect to the rotatable member.

3.6

Furthermore, for example, in the foregoing embodiment and modifiedexamples, the shaft member 13 (13A) is formed in one piece with thefirst rotatable member 11. However, the shaft member 13 (13A) may beformed in one piece with a rotatable member other than the firstrotatable member 11. If a joint structure includes three or morerotatable members as in the foregoing modified example, the shaft member13 (13A) may be formed in one piece with either of the two rotatablemembers arranged on the outermost side. Furthermore, the shaft member 13(13A) may be formed in one piece with any of those arranged between thetwo rotatable members arranged on the outermost side. In this case, theshaft member 13 (13A) is formed so as to extend in the axial directionfrom face portions on both sides of the rotatable member. Furthermore,the shaft members 13 (13A) may be formed in one piece respectively withthe two rotatable members arranged on the outermost side. In this case,the shaft members 13 (13A) extending from the rotatable members may beconfigured such that they can be coupled with each other throughscrewing or the like.

Furthermore, as shown as an example in FIG. 13 , the shaft member 13(13A) may be formed separately from the rotatable members. FIG. 13 is aperspective view schematically showing an example of a joint structure1D including a shaft member 13D formed separately from a first rotatablemember 11D. As shown as an example in FIG. 13 , the rotatable members(11D, 12D, and 18D) each have substantially the same configuration asthat of the second rotatable member 12 described above.

The shaft member 13D according to this modified example includes acircular ring-like base portion 133 and a cylindrical portion 134extending in the axial direction from the base portion 133. Thecylindrical portion 134 is formed so as to be substantially similar toin the shaft member 13 (13A) described above. That is to say, the lengthin the axial direction of the cylindrical portion 134 matches the totalof the widths of the rotatable members (11D, 12D, and 18D). Furthermore,the outer diameter of the cylindrical portion 134 is smaller than theinner diameter of the rotatable members (11D, 12D, and 18D) to theextent that the radial bearings 15 can be arranged. Accordingly, theradial bearings 15 are arranged between the shaft member 13D and therotatable members (11D, 12D, and 18D).

Meanwhile, the outer diameter of the base portion 133 is larger than theouter diameter of the cylindrical portion 134. Accordingly, the baseportion 133 is not allowed to be inserted into the through holes of therotatable members (11D, 12D, and 18D). In this modified example, arecess portion 117 provided at a face portion of the first rotatablemember 11D has the same diameter as the outer diameter of the baseportion 133, and the base portion 133 is fitted into the recess portion117 of the first rotatable member 11D. The base portion 133 may be fixedto the face portion of the first rotatable member 11D through screwingor the like. Note that the inner diameter of the base portion 133 is thesame as the inner diameter of the cylindrical portion 134.

As described above, the shaft member may be formed separately from therotatable members. In this case, as shown as an example in the foregoingmodified example, all the rotatable members (11D, 12D, and 18D) may beformed in the same shape. Thus, the production cost of the jointstructures can be reduced, which makes it possible to construct a linkmechanism of a robot at a lower cost.

As in the foregoing embodiment, the face portions of the rotatablemembers (11D, 12D, and 18D) may include recess portions with a shapethat allows the thrust bearing 14 and the encoder 16 to be accommodatedwhen the face portions are positioned facing each other. Furthermore, inthe foregoing embodiment and modified examples, the shaft member 13(13A, 13D) is formed so as to be hollow. However, the shaft member 13(13A, 13D) may be formed so as to be solid.

Furthermore, in the joint structure 1D according to this modifiedexample, the shaft member 13D is coupled with the first rotatable member11, and thus the radial bearings 15 arranged inside the through hole ofthe first rotatable member 11 may be omitted. The joint structure 1D onthe first rotatable member 11 side may be heavier by the weightcorresponding to the base portion 133 of the shaft member 13D beingarranged on the first rotatable member 11 side. Meanwhile, if the radialbearings 15 arranged inside the through hole of the first rotatablemember 11 are omitted, it is easy to make the entire weight balance ofthe joint structure 1D bilaterally symmetric.

3.7

Furthermore, in the foregoing embodiment and modified examples, a linkmember is individually coupled with a rotatable member. However, thecorresponding relationship between a link member and a rotatable memberdoes not have to be limited to this example. As in the modified examplesgiven as an example in FIGS. 10 and 13 above, if a joint structureincludes three or more rotatable members, coupling portions of at leasttwo rotatable members may be coupled with the same link member.

Hereinafter, an example thereof will be described with reference to FIG.14 . FIG. 14 is a perspective view schematically showing an example of astate in which a coupling portion of the first rotatable member 11 (11D)and a coupling portion of the third rotatable member 18 (18D) arecoupled with the same the link member 34. “Same link member” may beformed in one piece, or may be formed by combining a plurality ofmembers, as long as a plurality of rotatable members can besimultaneously driven.

As shown as an example in FIG. 14 , a link member 34 according to thismodified example is formed in the shape of a U with square corners, andhas end portions with the same configuration as that of the link member31. The link member 34 can be produced by coupling two link members 31as appropriate through welding or the like. The end portions of the linkmember 34 are coupled with the coupling portions of the first rotatablemember 11 (11D) and the third rotatable member 18 (18D). Accordingly,the first rotatable member 11 (11D) and the third rotatable member 18(18D) can be coupled with the same the link member 34. Note that thenumber of rotatable members that are coupled with the same link memberdoes not have to be limited to this example. Coupling portions of threeor more rotatable members may be coupled with the same link member.

In this manner, if coupling portions of at least two rotatable membersare coupled with the same link member, even when a relatively largeforce acts from the link member on the joint structure, the force can bedivided between and received by the plurality of rotatable members.Accordingly, deformation of the shaft member of the joint structure dueto an external force can be suppressed.

Note that the rotatable members that are coupled with the same linkmember may be selected as appropriate according to an embodiment. Forexample, as shown as an example in FIG. 14 , coupling portions of thetwo rotatable members arranged on the outermost side may be coupled withthe same link member. Furthermore, coupling portions of a pair ofrotatable members with one or a plurality of rotatable membersinterposed therebetween may be coupled with the same link member.Accordingly, a force that acts from a rotatable member arranged betweena pair of rotatable members coupled with the same link member can bereceived by the pair of rotatable members arranged on both sides. Thus,a force that acts on the joint structure can be prevented from beinglocally concentrated and be dispersed. Accordingly, it is possible toproperly suppress deformation of the shaft member of the joint structuredue to an external force, by selecting the rotatable members that arecoupled with the same link member in this manner.

3.8

Furthermore, as shown as an example in FIG. 15 , coupling between acoupling portion of a rotatable member and a link member may bereinforced using a reinforcing plate. FIG. 15 is a cross-sectional viewschematically showing an example of a joint structure 1E includingreinforcing plates 51 for reinforcing coupling between the couplingportion 21 and the link member 31. As shown as an example in FIG. 15E,the joint structure 1E according to this modified example includes tworotatable members (11E and 12E) as in the foregoing embodiment.

The face portions (111, 112, 121, and 122) of the rotatable members (11Eand 12E) include reinforcing plate-corresponding recess portions 511 to514 in the shape of a circular ring extending inward in the radialdirection from the outer circumferential face such that the reinforcingplates 51 substantially in the shape of a circular ring can be arranged.Except for this aspect, the rotatable members (11E and 12E) have thesame configuration as that of the rotatable members (11 and 12)described above.

The inner diameter of the reinforcing plate-corresponding recessportions 511 to 514 is the same as the inner diameter of the reinforcingplates 51. The inner diameter of the reinforcing plate-correspondingrecess portions (512 and 513) is larger than the outer diameter of therecess portions (115 and 126) such that a partition wall is providedbetween the reinforcing plate-corresponding recess portions (512 and513) and the recess portions (115 and 126). Accordingly, the innercircumferential walls of the reinforcing plates 51 and the thrustbearing 14 are prevented from being coming into contact with each other.The inner diameter of the reinforcing plate-corresponding recess portion514 is also larger than the outer diameter of the second recess portion127.

With this configuration, the reinforcing plates 51 are arranged adjacentin the axial direction to the coupling portions 21 respectively.Furthermore, the reinforcing plates 51 have an outer diameter that islarger than the outer diameter of the face portions (111, 112, 121, and122) of the rotatable members (11E and 12E). Thus, as shown as anexample in FIG. 15 , a pair of reinforcing plates 51 are arranged so asto hold the coupling region of the coupling portion 21 and the linkmember 31 from both sides in the axial direction and support thecoupling portion. Accordingly, the reinforcing plates 51 can reinforcecoupling between the coupling portion 21 and the link member 31.

That is to say, it is assumed that a moment in the axial direction(tangential direction) starting from the coupling region of the couplingportion 21 and the link member 31 acts on the link member 31. In thiscase, there is a possibility that a large force will act on the end face210 of the coupling portion 21, break the thick-wall portions 212, andcancel the coupling between the coupling portion 21 and the link member31. On the other hand, as in this modified example, if the reinforcingplates 51 are arranged adjacent in the axial direction to the couplingregion of the coupling portion 21 and the link member 31, such a forcecan be received by the reinforcing plates 51. Accordingly, a large forcecan be prevented from acting on the end face 210 of the coupling portion21, and thus the thick-wall portions 212 can be prevented from beingbroken. Accordingly, according to this modified example, it is possibleto produce a joint structure that is unlikely to be broken by twisting.

Note that the method for arranging the reinforcing plates 51 does nothave to be limited to this example, and may be selected as appropriateaccording to an embodiment. For example, it is also possible that thereinforcing plate-corresponding recess portions 511 to 514 as describedabove are not provided and the reinforcing plates 51 are directlyarranged along the face portions (111, 112, 121, and 122) of therotatable members (11E and 12E). The reinforcing plates 51 may be formedrespectively in one piece with the rotatable members (11E and 12E).Furthermore, in the foregoing modified example, the pair of reinforcingplates 51 are arranged on both sides in the axial direction of thecoupling portion 21. However, the reinforcing method using thereinforcing plates 51 does not have to be limited to this example, and,for example, either one of the reinforcing plates 51 may be omitted.That is to say, it is possible to produce a joint structure that isunlikely to be broken by twisting, by providing the reinforcing plate 51for supporting the coupling region of the coupling portion 21 arrangedat a side wall portion of the rotatable members (11E and 12E) and thelink member 31, on at least one of both sides in the axial direction ofthe coupling region.

Furthermore, in the joint structure 1E according to this modifiedexample, the joint structure 1E on the second rotatable member 12E sidemay be heavier by the weight corresponding to the radial bearings 15being arranged on the second rotatable member 12E side. Meanwhile, ifthe reinforcing plates 51 on the second rotatable member 12E side (onthe left side in FIG. 15 ) attached to the joint structures (11E and12E) are omitted, it is easy to make the entire weight balance of thejoint structure 1E bilaterally symmetric.

3.9

Furthermore, in the foregoing embodiment, the coupling portion 21 andthe link member 31 are coupled with each other via the wedge member 32.However, the method for coupling the coupling portion 21 and the linkmember 31 does not have to be limited to this example, and may beselected as appropriate according to an embodiment. For example, asshown as an example in FIGS. 16A and 16B, the coupling between thecoupling portion 21 and the link member 31 may be constituted by amagnet.

FIG. 16A schematically shows an example of a rotatable member 19 inwhich the coupling between a link member 31F and a coupling portion 21Fis constituted by a magnet. FIG. 16B is a partial cross-sectional viewtaken along the line C-C in FIG. 16A. The rotatable member is denoted bya reference numeral 19 for the sake of ease of description, and therotatable member 19 corresponds to, for example, the second rotatablemember 12 described above.

As shown as an example in FIG. 16B, the coupling portion 21F of therotatable member 19 has the same shape as the coupling portion 21, and arectangular soft magnetic plate 61 is attached to the groove portion 211of the coupling portion 21F. Meanwhile, the link member 31F has the sameshape as the link member 31, and a columnar permanent magnet 62 isarranged spanning between the groove portions 314. At this time, thepermanent magnet 62 is arranged such that its N pole is positionedtoward either one of the groove portions 314. The groove portions 314are provided with rectangular soft magnetic pins (63 and 64) that arearranged in contact with the permanent magnet 62. The soft magnetic pins(63 and 64) are fixed by a non-magnetic bolt 65.

Note that the material of the soft magnetic plate 61 and the softmagnetic pins (63 and 64) may be electromagnetic soft iron. The materialof the soft magnetic plate 61 and the soft magnetic pins (63 and 64) maybe selected as appropriate from among soft magnetic materials.Furthermore, the material of the non-magnetic bolt 65 may be selected asappropriate from among non-magnetic materials.

The soft magnetic pins (63 and 64) and the soft magnetic plate 61 arearranged such that they can be brought into contact with each other. Forexample, the soft magnetic plate 61 is arranged such that the end faceof the soft magnetic plate 61 is positioned close to the end face of thecoupling portion 21F. In a similar manner, the soft magnetic pins (63and 64) are arranged such that the end faces of the soft magnetic pins(63 and 64) are positioned close to the end face of the link member 31F.

Accordingly, when the soft magnetic pins (63 and 64) are brought intocontact with the soft magnetic plate 61, a loop of a magnetic force isformed by the permanent magnet 62, the soft magnetic pins (63 and 64),and the soft magnetic plate 61. Thus, the soft magnetic pins (63 and 64)and the soft magnetic plate 61 can be coupled with each other at anappropriate intensity. In this modified example, the coupling betweenthe coupling portion 21F and the link member 31F is constituted by amagnet in this manner.

According to this modified example, the coupling between the couplingportion 21F and the link member 31F is constituted by a magnet, and thusa link mechanism of a robot can be constructed without using tools.Accordingly, it is very easy to produce a robot.

Furthermore, when an excessive load is applied, coupling using a magnetis likely to be canceled. Thus, for example, if the coupling methodusing a magnet is used in a joint structure in which a force directlyacts from an actuator, such as the joint structures (408 a, 408 b, and408 c) of the robot 400, the link mechanism can be disconnected from theactuator when an excessive load is applied. Accordingly, accidents thatoccur when an excessive load is applied can be suppressed. In a similarmanner, in the case where the joint structure is used in an exoskeletalrobot, if the coupling method using a magnet is used in a jointstructure that acts on a human body, an excessive load that may damagethe human body can be prevented.

Note that, in this modified example, the permanent magnet 62 is arrangedon the link member 31F side. However, the arrangement of the permanentmagnet 62 does not have to be limited to this example, and the permanentmagnet 62 may be arranged on the rotatable member 19 side. Furthermore,as long as the loop of a magnetic force can be formed, the soft magneticpins (63 and 64) and the soft magnetic plate 61 may be partially made ofa non-magnetic material. Furthermore, the shape of each constituentelement may be selected as appropriate according to an embodiment. Forexample, the permanent magnet 62 may be formed in a rectangular shape.

Furthermore, a coupling portion and a link member may be coupled witheach other using a method other than a magnet. For example, in theforegoing embodiment, in a state where the end face 210 of the couplingportion 21 and the end face 310 of the link member 31 are arrangedfacing each other, the coupling portion 21 and the link member 31 arecoupled with each other. However, depending on the thickness of the linkmember 31 and the width of the groove portion 211, the coupling portion21 and the link member 31 may be coupled with each other in a statewhere the link member 31 is inserted into the groove portion 211.Furthermore, if each of the rotatable members includes a plurality ofcoupling portions, the coupling portions may be coupled with linkmembers using different methods.

3.10

Furthermore, in the foregoing embodiment, the thrust bearing 14 areaccommodated between the rotatable members (11 and 12) that are adjacentto each other in the axial direction, in order to receive a force thatacts in the axial direction from the rotatable members (11 and 12).However, the bearing that can be arranged between the rotatable members(11 and 12) that are adjacent to each other in the axial direction donot have to be limited to this example as long as they are ring-likebearing for receiving a force that acts in the axial direction, and maybe selected as appropriate according to an embodiment. For example,angular contact ball bearings capable of receiving a force in both ofthe thrust direction and the radial direction may be accommodatedbetween the adjacent rotatable members (11 and 12).

If a joint structure includes three or more rotatable members, a recessportion with a shape that allows the bearing to be accommodated (e.g.,the recess portion 115 and the first recess portion 126 of the foregoingembodiment) is provided between rotatable members that are adjacent toeach other in the axial direction. The recess portion for accommodatingthe bearing may be arranged on both sides or one side of faces that faceeach other (e.g., the second face portion 112 and the first face portion121 of the foregoing embodiment) of the adjacent rotatable members. Ifthe recess portion is provided on both sides of the faces that face eachother of the adjacent rotatable members, the heights (the lengths in theleft-right direction in FIG. 2 ) of the recess portions may be the sameor different from each other as long as they match the thickness of thebearing.

3.11

Furthermore, in the foregoing embodiment, the scale 161 is arranged onthe second rotatable member 12 side, and the detecting element 162 isarranged on the first rotatable member 11 side. However, the arrangementof the scale 161 and the detecting element 162 does not have to belimited to this example, and they may be switched. That is to say, thescale 161 may be arranged on the first rotatable member 11 side, and thedetecting element 162 may be arranged on the second rotatable member 12side. In this case, the wiring groove portion 114 is provided on thesecond rotatable member 12 side, and the output of the detecting element162 is taken out on the second rotatable member 12 side.

Furthermore, in the foregoing embodiment, the encoder 16 of the opticalreflection type is used. However, the type of encoder that can be builtin the joint structure 1 according to the present embodiment does nothave to be limited to this example, and may be selected as appropriateaccording to an embodiment. For example, the joint structure 1 may havea built-in encoder of the optical transmissive type.

The encoder of the optical transmissive type can be constituted by, forexample, a transmissive scale on which the optical transmittanceperiodically changes in the circumferential direction, and a detectingelement including a light-emitting portion and a light-receivingportion. In this case, it is possible to detect a relative rotationalangle between the adjacent rotatable members (11 and 12), by arrangingthe light-emitting portion and the light-receiving portion of thedetecting element such that light emitted from one face side of thetransmissive scale is received by the other face side.

Moreover, the joint structure 1 may include a magnetic-type orelectrical resistance-type encoder. For example, the magnetic-typeencoder can be constituted by a scale on which the magnetic forcechanges in the circumferential direction, and a detecting element suchas a Hall element for detecting the magnetic force. For example, as themagnetic-type encoder, a magnetic encoder (model No.: AEAT-6600-T16,etc.) manufactured by AVAGO can be used. Furthermore, as themagnetic-type encoder, a resolver (e.g., Singlsyn (registered trademark)manufactured by Tamagawa Seiki Co., Ltd., etc.) can be also used.

Furthermore, in the foregoing embodiment, the scale 161 is attached tothe plate 142 separately from the thrust bearing 14. However, theposition at which the scale 161 is attached does not have to be limitedto this example, and the scale 161 may be attached to the thrust bearing14. For example, if the housing washer (not shown) of the thrust bearing14 has a shape similar to that of the plate 142, the scale 161 may beattached to the end face of the housing washer. At this time, the washer141 may be omitted, and the shaft washer of the thrust bearing 14 may beallows to be directly in contact with the bottom face of the recessportion 115. Accordingly, the encoder 16 can be constituted using a partof the thrust bearing 14, and thus the number of parts and the number ofassembly steps can be reduced, and, moreover, the constituent elementsaccommodated in the internal space of the joint structure 1 can be madecompact.

Furthermore, in the foregoing embodiment, the scale 161 and thedetecting element 162 constituting the encoder 16 are arranged facingeach other in the axial direction. However, the arrangement of theencoder 16 does not have to be limited to this example, and, forexample, the scale 161 and the detecting element 162 may be arranged atthe outer circumferential wall of the shaft member 13 and the innercircumferential wall of the thrust bearing 14 such that they face eachother in the axial direction.

Furthermore, in the foregoing embodiment, the gap portion 116 in theshape of a circular ring is ensured such that the scale 161 and thedetecting element 162 face each other in the axial direction. However,the shape of the gap portion 116 does not have to be limited to thisexample as long as the scale 161 and the detecting element 162 can faceeach other in the axial direction, and may be selected as appropriateaccording to an embodiment. For example, the gap portion 116 may have asector-shaped cross-section.

Furthermore, if an optical encoder of the reflection type or thetransmissive type is used as the encoder accommodated in the jointstructure 1, an optical fiber may be arranged in the internal space ofthe joint structure 1, and the optical fiber may be used to emit andreceive light to and from the scale. In this case, an electrical signalcan be output via the optical fiber to the outside of the jointstructure 1, and thus the detecting element and the board may bearranged outside the joint structure 1. In this case, metal materialscan be eliminated from the constituent elements of the encoder built inthe joint structure 1. Furthermore, if the other constituent elementsare made of a resin, the joint structure 1 can be produced without usinga metal material.

Furthermore, in the foregoing embodiment, the detecting element 162transmits and receives an electrical signal by wire via the wiring board163. However, the method of the detecting element 162 for transmittingand receiving an electrical signal does not have to be limited to thisexample. For example, the detecting element 162 may transmit and receivean electrical signal wirelessly using a wireless module. In this case,the wiring board 163 may be omitted. In the foregoing embodiment, thewiring board 163 is extended from the internal space to the outside viathe wiring groove portion 114. However, the route of the wiring board163 does not have to be limited to this example, and the wiring board163 may be extended to the outside via the hollow portion 132 of theshaft member 13.

3.12

Furthermore, in the foregoing embodiment, the end face 210 of thecoupling portion 21 is provided with four protruding portions 213, sothat firm coupling between the coupling portion 21 and the link member31 is realized. However, the number and the shape of protruding portionsdo not have to be those in the examples of the foregoing embodiment, andmay be selected as appropriate according to an embodiment. Theprotruding portions provided at the end face of the coupling portion maybe designed as appropriate according to the end face shape of the linkmember that is coupled with the coupling portion.

Furthermore, in the foregoing embodiment, the protruding portions 213are formed in one piece with the end face 210. However, theconfiguration of the protruding portions 213 does not have to be limitedto this example, and may be selected as appropriate according to anembodiment. For example, the protruding portions 213 may be provided byforming holes in the end face 210 and inserting pins into the holes.

Furthermore, in the foregoing embodiment, the protruding portions 213are provided at the coupling portions 21. However, the positions atwhich the protruding portions 213 are provided do not have to be limitedto this example, and the protruding portions 213 may be provided at theend face 310 of the link member 31. In this case, if the end face 210 ofthe coupling portion 21 is provided with holes for receiving theprotruding portions 213, the coupling portion 21 and the link member 31can be coupled with each other as described above.

3.13

Furthermore, in the foregoing embodiment, the wiring board 163 of theencoder 16 is extended to the outside from the first rotatable member 11side. However, the direction in which the wiring board 163 is extendedto the outside does not have to be limited to this example. For example,if the detecting element 162 is arranged on the second rotatable member12 side, a wiring groove portion similar to the wiring groove portion114 may be provided in the second rotatable member 12, and the wiringboard 163 may be arranged so as to be extended to the outside from thesecond rotatable member 12 side. Furthermore, both of the rotatablemembers (11 and 12) may be provided with the wiring groove portions 114,and the direction in which the wiring board 163 is extended to theoutside may be selected according to a situation in which the jointstructure 1 is to be used.

3.14

Furthermore, in the foregoing embodiment, the end faces of the couplingportions 21 arranged at the side wall portions (113 and 123) of therotatable members (11 and 12) are formed as flat faces, except for theprotruding portions 213. However, the shape of the coupling portions 21does not have to be limited to this example.

FIG. 17 shows a modified example of the shape of each coupling portion21. A rotatable member 11G shown in FIG. 17 is formed so as to besimilar to the first rotatable member 11, except for a coupling portion21G. Furthermore, the coupling portion 21G is formed so as to be similarto the coupling portion 21, except for the shape of its end face.Furthermore, a link member 31G is formed so as to be similar to the linkmember 31, except for the shape of its end face.

In this modified example, a recess portion recessed in the longitudinaldirection is provided at the center of the end face of the link member31. In conformity with this aspect, the coupling portion 21G arranged ata side wall portion of the rotatable member 11G is configured so as tohave a projecting portion 2101 projecting outward in the radialdirection at the center in the tangential direction. Furthermore, at theend face of the coupling portion 21G, the positions on both sides of theprojecting portion 2101 are formed as flat faces that are slightly lowerthan the projecting portion 2101, and the protruding portions 213 arearranged at these portions. Note that this coupling portion 21G can beapplied not only to the first rotatable member 11 but also to the secondrotatable member 12.

According to this modified example, in each coupling portion 21G, thelength in the radial direction of the thick-wall portions can be madeshorter by the length of the projecting portion 2101 being provided.Thus, in this modified example, the position of the groove portion intowhich the head portion 321 of the wedge member 32 is inserted can bechanged slightly to the outer side in the radial direction, comparedwith the foregoing embodiment. Accordingly, the internal space of thejoint structure can be increased, and thus a bearing with a largediameter can be arranged inside and the strength of the joint structurecan be improved. Furthermore, since the diameter of the hollow portionof the shaft member can be increased, the joint structure can be madelighter. Furthermore, since the outer diameter of the shaft member canbe increased, the rigidity of the shaft member can be improved.

3.15

Furthermore, in the foregoing embodiment, the thrust bearing 14 and theradial bearings 15 are used as bearings that are arranged inside thejoint structure 1. However, the bearings that can be used do not have tobe limited to these, and may be selected as appropriate according to anembodiment.

FIG. 18 shows a modified example using a bearing different from that inthe foregoing embodiment. A joint structure 1H given as an example inFIG. 18 includes a first rotatable member 11H and a second rotatablemember 12H. The first rotatable member 11H is formed so as to besubstantially similar to the first rotatable member 11, and the secondrotatable member 12H is formed so as to be substantially similar to thesecond rotatable member 12.

The recess portion 115 of the first rotatable member 11H is formed inthe shape of a circular ring, and the base of an inner circumferentialface 1151 of the recess portion 115 is provided with a step portion 1152in the shape of a circular ring extending inward in the radial directionfrom the inner circumferential face 1151. Meanwhile, the first faceportion 121 of the second rotatable member 12 that faces the recessportion 115, the second rotatable member 12 being adjacent to the firstrotatable member 11H, is provided with a projecting portion 1211 in theshape of a circular ring with a diameter smaller than that of the recessportion 115 and the step portion 1152. Furthermore, the base of an outercircumferential face 1212 of the projecting portion 1211 is providedwith a step portion 1213 in the shape of a circular ring extendingoutward in the radial direction from the outer circumferential face 1212of the projecting portion 1211.

In this internal structure of the joint structure 1H, a cross rollerbearing 71 in the shape of a ring is arranged so as to be supported bythe inner circumferential face 1151 of the recess portion 115, a facealong the axial direction of the step portion 1152 of the recess portion115, the outer circumferential face 1212 of the projecting portion 1211,and a face along the axial direction of the step portion 1213 of theprojecting portion 1211. The cross roller bearing 71 can receive a loadthat acts in the axial direction and the radial direction on the jointstructure 1H. Note that, if three or more rotatable members areprovided, this structure having such a built-in bearing may be providedin each gap between two adjacent rotatable members.

According to this modified example, the following effects can beachieved. That is to say, typically, the inner diameter of the crossroller bearing 71 is larger than the inner diameter of the thrustbearing. Thus, in this modified example, an available region inside thebearing is wide. Accordingly, for example, the outer diameter of theshaft member 13 can be increased, and thus the rigidity of the shaftmember 13 can be improved. Moreover, the radial bearings 15 with a largediameter can be used, and thus a load that is received by the radialbearings 15 can be increased. Furthermore, the diameter of the hollowportion of the shaft member 13 can be increased, and thus the jointstructure can be made lighter.

LIST OF REFERENCE NUMERALS

-   -   1 Joint structure    -   11 First rotatable member    -   111 First face portion    -   112 Second face portion    -   113 Side wall portion,    -   114 Wiring groove portion    -   115 Recess portion    -   116 Gap portion    -   12 Second rotatable member    -   121 First face portion    -   122 Second face portion    -   123 Side wall portion    -   124 Through hole    -   125 Interlock projecting portion    -   126 First recess portion    -   127 Second recess portion    -   128 Projecting portion    -   129 Wire-driving groove portion    -   13 Shaft member    -   131 Fastener    -   132 Hollow portion    -   133 Base portion    -   134 Cylindrical portion    -   14 Thrust bearing    -   141 Washer    -   142 Plate    -   143 Hole portion    -   15 Radial bearing    -   16 Encoder    -   161 Scale    -   162 Detecting element    -   163 Wiring board    -   164 Projecting portion    -   165 Connector portion    -   17 Cable    -   171 Connector portion    -   21 Coupling portion    -   210 End face    -   211 Groove portion    -   212 Thick-wall portion    -   213 Protruding portion    -   214 Bottom portion    -   31 Link member    -   310 End face    -   311 Hole portion    -   312-313 Through hole    -   314 Groove portion    -   315 Edge portion    -   32 Wedge member    -   321 Head portion    -   322 Body portion    -   323 Through hole    -   324 Tapered portion    -   33 Screw    -   331 Head portion    -   332 Tapered portion    -   333 Male thread portion    -   400 Robot    -   401 Base    -   402 Support    -   403-404 Actuator    -   405-406 Movable portion    -   407 a-407 h Link member    -   408 a-408 f Joint structure    -   409 Front end portion    -   410 Robot    -   411 Link member    -   412 Joint structure    -   413-414 Fixture    -   415-416 (Bowden) wire    -   417 Binding member    -   420 Delta robot    -   421 Base portion    -   422 Rotary motor    -   423 a-423 e Link member    -   424 Joint structure    -   425 Front end portion    -   426 Link portion    -   420A Delta robot    -   427 Linear motor    -   1A Joint structure    -   13A Shaft member    -   18 Third rotatable member    -   1B Joint structure    -   11B First rotatable member    -   111B First face portion    -   21B Coupling portion    -   400C Robot    -   1C Joint structure    -   31 c Link member    -   1D Joint structure    -   11D First rotatable member    -   117 Recess portion    -   12D Second rotatable member    -   13D Shaft member    -   133 Base portion    -   134 Cylindrical portion    -   18D Third rotatable member    -   34 Link member    -   1E Joint structure    -   11E First rotatable member    -   12E Second rotatable member    -   51 Reinforcing plate    -   511-514 Reinforcing plate-corresponding recess portion    -   19 Rotatable member    -   21F Coupling portion    -   31F Link member    -   61 Soft magnetic plate    -   62 Permanent magnet    -   63-64 Soft magnetic pin    -   65 Non-magnetic bolt

What is claimed is:
 1. An externally-driven joint structure comprising:a shaft member that extends in an axial direction; and a plurality ofrotatable members that are arranged along the axial direction, and arecoupled with each other by the shaft member in an axially rotatablemanner, wherein each of the rotatable members comprises: a pair of faceportions that are parallel to each other in the axial direction, a sidewall portion that is arranged along outer circumferential edges of thepair of face portions, and at least one coupling portion that isarranged at the side wall portion, and is coupled with a link memberconstituting a link of a robot, and wherein the face portions of each ofthe rotatable members are provided with a recess portion with a shapethat allows a bearing in the shape of a ring that receives a force thatacts in the axial direction to be accommodated between rotatable membersthat are adjacent to each other in the axial direction, and the sidewall portions of the rotatable members are formed in the shape of acylinder, and the coupling portions arranged at the side wall portionshave a shape obtained by cutting, in a tangential direction that isperpendicular to a radial direction of the side wall portions, arcportions of the side wall portions.
 2. The externally-driven jointstructure according to claim 1, wherein at least one rotatable member ofthe plurality of rotatable members comprises a plurality of the couplingportions arranged at the side wall portion.
 3. The externally-drivenjoint structure according to claim 1, wherein an encoder for detecting arelative rotational angle between the rotatable members that areadjacent to each other in the axial direction is further accommodatedbetween the recess portions of the adjacent rotatable members.
 4. Theexternally-driven joint structure according to claim 1, wherein therecess portions are formed in the shape of a circular ring, bases ofinner circumferential faces of the recess portions are provided with astep portion in the shape of a circular ring extending inward in aradial direction from the inner circumferential faces, a face portion ofa rotatable member that faces the recess portions, the rotatable memberbeing adjacent to the rotatable members, is provided with a projectingportion in the shape of a circular ring with a diameter smaller thanthat of the recess portions, a base of an outer circumferential face ofthe projecting portion is provided with a step portion in the shape of acircular ring extending outward in the radial direction from the outercircumferential face of the projecting portion, and a cross rollerbearing as the bearing in the shape of a ring is arranged so as to besupported by the inner circumferential face of the recess portion, aface along the axial direction of the step portion of the recessportion, the outer circumferential face of the projecting portion, and aface along the axial direction of the step portion of the projectingportion.
 5. The externally-driven joint structure according to claim 1,comprising two rotatable members, wherein the coupling portions of therotatable members are arranged symmetric about the axial direction suchthat, even when the joint structure is reversed about an axis that isperpendicular to the axial direction, the joint structure can be usedwhile a positional relationship between the link members is maintained,one of the two rotatable members is formed in one piece with the shaftmember, the other rotatable member of the two rotatable members has athrough hole into which the shaft member is allowed to be inserted, anda radial bearing is arranged so as to be interference-fitted to theshaft member and clearance-fitted to an inner circumferential wall ofthe through hole, or so as to be clearance-fitted to the shaft memberand interference-fitted to the inner circumferential wall of the throughhole.
 6. A link mechanism comprising: two or more joint structuresaccording to claim 5; and the link members that are coupled with each ofthe coupling portions of each of the joint structures, wherein two jointstructures that are adjacent to each other via the link member arearranged such that one of the joint structures is used in a state ofbeing reversed about an axis that is perpendicular to the axialdirection with respect to the other joint structure so that the tworotatable members of each of the two joint structures face each other inthe direction that is perpendicular to the axial direction.
 7. Theexternally-driven joint structure according to claim 1, comprising threeor more rotatable members, wherein the coupling portions of at least tworotatable members of the three or more rotatable members are coupledwith a same link member.
 8. The externally-driven joint structureaccording to claim 1, wherein coupling between the coupling portions andthe link member is constituted by a magnet.
 9. The externally-drivenjoint structure according to claim 1, wherein the side wall portions ofthe rotatable members have a height that matches a thickness of the linkmember.
 10. The externally-driven joint structure according to claim 1,wherein the coupling portions arranged at the side wall portions have aprojecting portion projecting outward in a radial direction at a centerin the tangential direction that is perpendicular to the radialdirection of the side wall portions, in conformity with a recess portionprovided at a center of an end face of the link member.
 11. Theexternally-driven joint structure according to claim 1, wherein areinforcing plate for supporting a coupling region of the couplingportion arranged at the side wall portion of the rotatable member andthe link member is provided on at least one of both sides in the axialdirection of the coupling region.
 12. A link mechanism comprising: thejoint structure according to claim 1; and the link member that iscoupled with the coupling portion arranged at the side wall portions ofthe rotatable members of the joint structure, wherein the side wallportions of the rotatable members of the joint structure comprise awire-driving groove portion, a fixture is attached to the link member,and a wire that is driven by an external drive source is arranged alongthe wire-driving groove portion, and the end portion of the wire isfixed to the fixture.